I've often ejected players when doing a map change either because
a) they are AFK
b) they don't respond to the warnings
c) doing a map change when you're online may lockup Windows ME/98 workstations
If they happen to sneak in during a setup, I let them stay as long as they don't mess around (I.e. take a Me-262 up cause I haven't turned if off yet).
Other than that, I've never had to eject a player.
Maybe Admin function should ask for their password as a check before allowing rights? This would resolve any 'accidental' logins with cousins, wives, and friends.