I keep my computer on all day. It goes on at about 6.00 am and off at about 9.00 or 10.00 pm. I let it go through the shutdown procedure and then I switch off at the mains. It does no harm to leave it on all the time and I have it scheduled to go into standby after 5 hours with the monitor standby at 3 hours and disks at 4 hours.
Other people keep their machines on all day every day. I don't as my "office" is near my bedroom and the sound, although not loud, is enough to distract me at night.
What computers don't like is being switched on and off many times in a short(ish) period. This applies especially to monitors where large voltage surges during switching can reduce the life of some components.