Some have come to the conclusion that it is better to switch everything
off if the macine is going to be unused for more than 4 or 5 hours.
There is a tradeoff involved, thermal shock vs continual erosion of
traces, extra cost of machine repair from surge at power-up vs power
load at idle.

This question can generally be counted on to start a flame war. People
have strong opinions and there has been little investigation to prove
the results either way.