Leave pc on ovenight or shut it down

This is pretty much just a personal preference thing. I personally leave my system on but make sure the display is set to blank when not being used. I do that because I often want to access files on my system from other machines I own.

From a cost standpoint, it will cost more to leave it on all the time then to shut it down when you’re done for the day.

As far as the computer longevity, I don’t think it will make a big difference either way.
I tend to leave mine on throughout the day and depending on whether I plan on using it the following day either put it in sleep mode or shut it down entirely. I’ve been doing this for all my machines and not had one fail prematurely (other than in the early 00s with the bad caps on motherboards and PSUs but not much could be done about that…)