We can classify users according to a quality in common by grouping them. For example, we can create user groups for representing the structure of a company.
Groups allow you to speed up the process of defining permissions on projects. Also it is possible to grant permissions to an entire group, instead of doing it individually (see section 3.3).
In this way, if we want a group has access to a folder to give permissions to the whole group instead of doing it user by user.