With my old computer that I still have, I once got into the habit of turning off the screen and leaving the computer on all the time. The first couple of times I didn't even notice it, and then once I just kept on doing it over and over again, and then one day I realized I hadn't turned off my computer for almost a month.
I never had any issues with my computer or anything. But it got me thinking about how bad it might be with the fans and everything constantly running all the time with the heat and things.
I was lucky and nothing was ever wrong with my computer, but it's always good to maybe have it looked at just to be on the safe side.