I must say I came across this concept only very recently when a company advertised this new policy in their organization on Linkedin. As expected from the comments section, the people were divided on whether it made sense or not. As is always the case, there are two sides to the coin and you would agree or disagree depending on the side you are on.
There are days in a month where women feel unwell when they are going through the menstrual period. And this may affect them in terms of their efficiency of doing the various tasks. So a policy like menstrual leave enables them to rest and relax without having to worry about meeting their deadlines for completing a certain task. It also shows an organization’s empathy in understanding the concerns of a woman employee.