Frankly, I don't think PC electronics suffers from a nightly shutdown as even 365 cycles a year is still very small for thermal cycling stress. And if it can't take the electrical transients, it hasn't been designed correctly. My only exception would be PCs with older hard disks that have the brown oxide coating.
Well, I was not referring to thermal or transients, as much as I was current inrush, as a problem. You see this specifically with poorly made PS's on clones and secondary brand PCs, but it happens more than I care for. The overcurrent suppression is just inadequate, and overtaxes all of the rails.
This may have never happened to you, for which I am happy, but it happens to many, specially when living in an area (like I do) where the mains are always overvoltage (or under) and throwing a lot of spikes (so I guess partially, I was talking transients), like when you know you've got a bad utility, when you can sit there and watch light bulbs popping out on you every few days.
Upshot is, no problem leaving it on if you have good battery backup to do all of the pre-filtering for you...