IntroductionRead More Here
To be able to load faster, the games stores data in so called cache files. The game checks on startup if those files are available and if so, they are loaded. If they are not available, they are created.
Over time these files accumulate out-of-date data (especially if you use custom content and mods) and because of this, it’s best to delete them from time to time (just as you delete your browsers cache from time to time)