Imagine a computer like a person. As you get tired you start to make mistakes. The more tired you are, the more mistakes you make and those mistakes stack up and lead to other mistakes. Little brain facts, clumsiness, not paying attention, etc. Sleep is a good reset of your mind and you wake up well rested.

Computers are similar. They start to have little mistakes as temp memory gets filled up over time. A power cycle resets that temp memory and clears any junk. Gives the computer a good night's sleep.