You can aggregate users in several groups and this is useful to exploit advanced functions inside the learning manager.
These functions are:

• Learning object visible only to certain groups
• Messages sent only to certain groups
• Forums are visibile only to certain groups
• Advices visible only to certain groups
• Filtering stats and reports by groups.
  

For the Project Manager module the Group usage is Mandatory.

Note: Classroom groups are not related to admin groups. Grouping users in classrooms means manage these kinds of functions:

• Forum: Some forum discussion categories could be seen by one or more groups
• Messages: It's possible to manage the receivers by groups
• Advice: It's possible to show advices to one or more groups
• Learning Objects: Some learning objects can be shown only to some groups
• Statistics: We can create group filterss for watching statistics data
• Project: It is mandatory to assign a project to one group