Currently its not possible to see what Permission Schemes a user Group is being used for.

1) This means its difficult to work out if a group is not being used at all (makes it hard to clean up groups - something required over time).

2) This means its difficult to audit what permissions a given user has.
You can see what groups they are a member of - but then you have to go through all the permission schemes to see where (if at all) each group is being used.

3) Its not easy to spot a group being used in the wrong permission scheme.
Perhaps the result of a mistake - it means that suddenly a user can see a project (or a whole lot of projects) that they shouldnt.