My company sent me on a computer maintenance course in London many years ago and this was one of the first things we covered. Most tech guys say the same thing these days when folks have problems with their computer "have you tried shutting it down and turning it back on again?" This simple act still cures many folks problems with PC's (and Macs).
It's of no consequence to home users but the last two companies I've worked for over the past 24 years both had the same policy, that all computers were switched off when staff went home in the evening. Computer equipment was kept for 3 - 6+ years depending on status and by far the biggest number of malfunctions (of computers) were DOA's.