But there is still SOME expantion and contraction because the temps will change depending on what you do, but not as much as turning it off and turning it on which can be as big as a 40F degree change in temp from room to medium-max temps.... Sometimes even more.. but my temps are never 10F above room temp... And even after that they dont change more than 5F....
I always keep my PC on 24/7. It's a good choice, because it won't damage your hardware. But, I don't thimk this happens to you guys, my PC slows down after a few weeks. A nice healthy reboot always helps though . I don't recommend this if your PC is in your bedroom and have a noisy fan. My fan is so noisy. CAN"T SLEEP!!!!