If you have a system you can reboot at will, go nuts! It's rather like
driving your car faster because you're tired and want to get home before you
fall asleep at the wheel... It's seldom opportune. If CPU time is too
limited, that's a probably hardware problem first and foremost, rather than
a system admin problem.
When might it be necessary? You have a process running that you cannot kill
outright, and you either want it to allow other processes to run, so you
give it a lower priority, or, you want it to run in preference to other
processes, so you give it a higher priority. Or you have a process running
that you want to run only when the system is idle, so you set its process to
low. Or you have a CUP-hogging process that you literally cannot kill
(access denied), but which will let you reset its priority.
Googling 'windows 2000 "task manager" "set priority"' returns 416 English
language hits, so plenty of sites have something to say about this. Adding
site:microsoft.com reduces this to six. One of those is
http://www.microsoft.com/technet/prodtechnol/windows2000serv/maintain/monitor/03w2kada.mspx
