Groups are used to be allowed to view or edit not only their own documents but also those of a group. Typical groups could be, for example, the accounts payable department or the production department. Thus, Maximiliane Muster could be assigned to the Accounts Payable group. Under 'New files with owner' Maximiliane Muster could be assigned to the group and with access 'Read public, edit own' she can handle the files of Accounts Payable like her own - and her colleagues can do the same.
The field 'Group(s)' is not a separate category of rights assignments. Rather, 'Group(s)' specifies other users for which specific permissions are set. It can be recommended that these group users be created with capital letters, for example (e.g. PURCHASE,SALE). This makes it easy to see visually that these users are managed primarily or only for specific access rights (groups).