A user with Super'User' rights can do anything in RT.
I think you know what it means to be an SuperUser. You don't need more rights. It's powerful and useless at the same time.
Why is the SuperUser right bad:
- It's absolute power and power can break things, absolute power can break more things
- It's hard to check restrictions for other users
- Even if you are an administrator you should live in the same enviorment as your users to know how bad their live is
NOTE: Starting from version 3.2(or 3.4?) RT doesn't show users with the SuperUser right in a ticket owner select-box. (When you are logged in as a SuperUser, other SuperUsers appear in the owner selection box, but when you are logged in as a privileged user (not as SuperUser) the other SuperUsers do not appear in the selection box. This is normal).
NOTE: Think about this right as "right for main administrator(s)". Administrator can be an user of the RT at the same time, but you should grant him rights as you grant them to other users, because RT hides "super users" from interface in several cases. For now it's only hiding SuperUsers in the ticket owner select-box (see previous note), but in the future version there could be more such exceptions in RT because it's the right thing to do.