Currently two different types of user groups are available. Project level user group and a System level user group

    In their respective articles  the difference between them can be seen, but a general  recommendation is to use the system level user group when for example multiple syndicated studies setup in different projects where a group of users should have access to all these projects. 

    In cases where you would like to streamline user maintenance and improve sharing within a single project use the project level user groups.