Nobody can tell you anything without proper system info or other technical details like version of AE and cache settings.
You can set AE to use less room on the hard drive for its cache. I wouldn't clear it if you didn't have to since it makes working with projects faster when you open them again.
Mylenium - this is a general question and I am guessing most recent Ae versions have cache options.
Szalam - thank you for the tip, I know where you are coming from as an artist - you'll need to get back at a certain project and the cache is right there where you left it, but, I am asking this as a trainer, it would be nice to have an option (a tick mark) somewhere in the pref to clear the cache as soon as you quit the app. Ae does suck a lot of HDD/SSD space.