The differences between admin and non-admin users are not explicitly documented. This regularly but persistently leads to confusion among (novice) users. The latest case I noticed is most-likely message#57479.
I think it would be good to have a document (section) containing a clear description of at least:

• the behavior of (project) permissions for admins
• the behavior of workflow status transitions and fields permissions for admins
• the differences between (the behavior of) front-end features for admins and non-admins (like issue-copy targets, groups display on profiles, etc.)

I think a good way to start on this would be to search all commit messages for an 'admin' string and see if each of the results then actually relates to any functional difference, which if it does then needs to be described.