I would turn it off. These days, harddrives are robust enough to take this
activity especially if you only do it once or twice a day. If you do not
occasionally turn it off, Windows never has a chance to refresh itself and
you most likely will start having problems with running software in the long
run. Granted, using the later versions of Windows like XP and 2000, this is
less of a concern but it is good to do none-the-less.
Good luck.