It’s an age old question answered by experts who still do not agree. Simon Hill:
The idea that you should avoid turning your computer off at night is pretty popular: After all, frequent shutdowns and start ups are going to have an impact on the components and wear them out faster. Aren’t they? On the other hand, you’d imagine having your computer running all the time is going to contribute to wear and tear as well, wouldn’t you?
So, it the end, it depends. If you use it all day, don’t turn it off for brief periods. If you use it for a few hours only, turn it off.