it should only run for a minute at start-up though it has been known to pop up and run at other random times. this is why many prefer to turn it off.
if you don't search your pc for files often, then turning it off won't hurt anything at all. you can still search your pc for files and such without it but it does take a lot longer to complete.
if it's getting in the way, then turning it off is a valid option that won't effect normal pc performance or operation at all. i have it turned of on my pc's as well. pretty much never search for files so it is just not needed on my systems.