A cool feature of Azure AD is Access review. It can be used for many things to control Azure AD group membership. One of the things I will be using it for is to control licenses and help to provide self service license management.
With Access Review we can control how often the users or owners are prompted to re-validate if the still need access to the group. This can be weekly, montly, quarterly or yearly. Once this period is over the users will be prompted via email to review their access to the group. We can even control what behavior will happen if the fail to do so.