Some people might not understand the need for the last part of this phrase: "in a way that benefits society." There are ways of encouraging people to work less that do not benefit society, which is a detail which is sometimes lost in questions like "does it help poor people when rich people work less?"
First: can it be helpful to society at all if people work less? Biggest reason to think the answer is no is war. Iran was just fighting the US and Israel. The fighting stopped; a day ago, US President Trump posted a promotional picture for a fighting match between two people. Is this relevant? Question: does it matter if the world thinks Iran won the fighting against the US, which Iran's leadership council said is not over? (Israel also played a role of course, but the US spends much more on military than Israel, and it's likely that the US sank the majority of Iranian naval vessels etc. Basically all I know is that Trump mentioned an island, so I looked it up on Wikipedia, and Iran uses it to export oil, and the article mentioned strikes by the US on the island; not strikes by Israel. The US has aircraft carriers, Israel doesn't.)
If it does matter whether the world thinks the US lost the war, presumably by being overwhelmed by cheap drones, then the war is like the martial arts match, which is held to determine a winner, I think (I have no interest in watching people hit each other and so I can't say whether people care more about the action than the results).
So: other possibilities in which people work less, and why they would not benefit society. (These are basically ways that other people have thought of, without thinking of this idea.)
Possibility: there is no unemployment. Actually making a plausible scenario for this condition is hard. Suppose a rule, "rich people must spend as much money per year as they earn, or they will be executed." Not realistic because in reality, people like to save money during part of their lives, then spend it when they get older. People also like to give money to their children. So, are rich young heirs forced to work, so that there is no unemployment? In general, an economy is likely not to be perfectly balanced so that there is absolutely no change in any macroeconomic indicators, like percent of wealth held by the top 10%, from one year to the next. If wealth is increasing, then even if there is no unemployment at one point in time, it would arise in the future, if a scenario is simulated for thousands of years.
We just ignore that and say that there is no unemployment. If there IS unemployment, then if people work less, then it allows other people to work, which reduces unemployment, which drives up wages. This is basically the case no matter what the details are regarding people working less. So it becomes harder to show that people working less in this situation helps society. If any methods show benefit under this condition of no unemployment, they will show a larger benefit if there is unemployment.
Possibility: welfare. People quitting work and just collecting welfare, paid for by rich members of society. By many metrics, society would be improved by this: if you exclude the people who are deliberately not working and who are collecting welfare, then more people can find jobs, because someone has to create the value which is consumed by the people on welfare. But on a fairness metric, this is worse: it does not benefit society. Someone who doesn't care about fairness, or who believes in an ancestral debt that can only be paid off by welfare, might disagree and say that it does benefit society.
Possibility: people who value their time highly, and value more money lowly, make a sacrifice in working less time. Example: someone who works 60 hours per week and makes $2 million per year reduces their work load to just 40 hours per week and makes $1 million per year. They have to work 33% more to make $1. Maybe this increases the time they spend with their children from 1 hour per week to 10 hours per week, a 900% increase, and they feel it's worth it. But it doesn't benefit society for them to do this. Natural assumption is that if they are working 67% of the hours, they are still providing 67% of the value to their company. Informed conclusion is that they are still providing even more than 67% of the value, since people are less efficient when they work more, though the actual relationship between time worked and efficiency while working probably has a peak (like with the model of, 'efficiency is quadratic due to a split between information gathering and decision making, with the value of decisions being directly proportional to the information gathered').
So if they are providing 67% of value, while earning only 50%, then the company is earning more. Even if they're making $1 million per year, most stocks are held by rich people, and it's reasonable to say the higher profits for the company go to rich people. Result: higher inequality. If rich people have more, then poor people have less; if everyone has more money it's just called inflation. This first-order effect is bad for society, and the second-order effect of "creating a pattern for other people to follow" is also bad for society. If one worker is willing to sacrifice and work more for lower wages, then companies will expect other workers to do the same.
Possibility: no sacrifice, people just work less with a proportional reduction in wages. The $2 million per year worker goes to $1.33 million when they reduce their hours per week from 60 to 40. In reality, people tend to work based on how they are paid, with exceptions for stupid people who don't realize when they're being paid more than other people who are doing the same amount of work.
So if the worker is being paid 67% as much, then they will only try to do 67% of the original work. They might 'accidentally' do more, just as when they are only getting paid 50% as much (and still looking at being granted the option of doing this as a favor from the company), but they won't feel an obligation to do so.
As the middle option, that seems like it's being fair to all involved, it can be hard to see why this is bad for society. It's basically only bad because it's not stable. There is nothing that makes it particularly attractive, either for the company or the worker, and so not many people would do it. All it really does is exist as what seems like an acceptable solution, which prevents people from looking for a better solution. If unemployment exists, then people working less in this way does reduce unemployment, but people often talk about things like the non-accelerating inflation rate of unemployment, which is basically an excuse to ignore all the young people who can't find jobs despite a low birth rate: an excuse because inflation can't happen, or eventually ends, without the first step of printing money. So if people don't see reducing unemployment beyond a certain point as important, then the benefits to society from people working less in this way cease.
Possibility: people work less but are paid the same amount. Workers say they want this but it provides no benefit to a business. Like with welfare, it's a solution that involves conflict: one side benefits, while another side receives net harm (as opposed to just a smaller benefit). Conflict rarely generates solutions better than the best possible solution that doesn't involve conflict.
Possibility: instead of getting people to work less, businesses find ways to get people to work more. This increases unemployment and also increases inequality, because people won't demand wage increases in proportion to the amount of work they do.
The final possibility is this idea. If we use the same terms as before, businesses are making a sacrifice: the $2 million per year worker goes from 60 to 40 hours per week, and is paid $1.5 million, rather than $1 million (worker sacrifices) or $1.33 million (proportional reduction). The potential for this to benefit society, ignoring the effects that the worse possibilities mentioned above can also provide (like lower unemployment), is rooted in people working harder because they are being paid at a higher rate; or alternatively, people working harder because if they complete tasks sooner, they have more free time. Businesses benefit if people work harder, and have the option of preventing people from working less in this way if the promised efficiency gains don't materialize (including by truthful indications to workers that the business will shut down due to unprofitability if workers don't provide enough value to the company). Businesses also have a safety mechanism if giving workers more freedom to decide when tasks are done leads to people doing a worse job on tasks by spending less time on them (i.e. dishonesty): people who finish tasks earlier so they can leave work will be paid less.
