Because I have already tried to get teachers to stick to a seating plan in their lessons before, they just don't do it. Then there is the non ICT subjects that book whichever room is available for their lesson.
I use roaming profiles with redirected appdata. There can be some pretty large folders in there which cause slow login times. Local profiles just won't work here though so I am currently going through and finding all of the worst offending folders and trialling a GPO that excludes them from syncing in a roaming profile.