Some people might be able to relate to this better than others. For those have and can relate, you'll now how difficult it is to find things. Sure, you know where most things are, because they're always exactly where you left them, but try to find something you haven't used since 6 months ago. You can't do it, can you.
Computers too suffer from big messes.
Only the effect on your computer is far worse than it is on you. When your computer lives in a mess it starts to slow down, do silly things, and sometimes serious things, like corrupting your files, becoming unreliable, and generally being very painful. Just like you, your computer needs someone to clean up after it. Your computer tends to make messes, even while your busy making one of your own. Without maintenance and cleaning, things can get out of hand.