Short answer: No reason what so every NOT to shut down your PC over night, with the exception of some needed functions of said PC. For example it's a server of some sort..or you run your home security off your PC. Something that requires you PC to be left on.
I shut mine down every night..and I'm one of those that keeps a PC for 3 to 5 years before upgrading. Can't afford to upgrade every year like some. This last upgrade I built my own PC and gave my old one to the wife (as she's gotten into looking up craft stuff online, and ebaying) and it's over 5 years old now with no upgrades other then adding another hard drive. The original hard drive is still the main drive. It's a Dell PC btw. My son has an even older one (Toshiba desktop, that should tell you how old) and it's still working too, although not much use anymore. All was shut down at night, unless I had some long downloading or maintenance to be done overnight, which was rare. So I can say with reasonable certainty that shutting down the PC does NOT cause it extra wear. In fact I would think it would be the other way around.. leaving it running all the time would be extra wear.
Usage: I use to be a big time gamer. Was even a clan leader for SOF2 for years. I used the PC's everyday. I'm nutty about defragging and scanning for nasties as well as cleaning old files no longer needed. So, I can say I'm well above average on the usage of the PC. I even like to reformat every so often just to get a fresh start
Disclaimer: This is my opinion from years of observation, but I'm not a computer expert or engineer.
