I've got 146GB of System Temporary Files.

I ran CCleaner for the first time today, and it's coming up with 146GB of System - Temporary Files. I'm not sure what exactly is causing it, but when I go on detailed results, most of it says After Effects, not sure why. I'm afraid of running cleaner in case it screws something up. It's also showing 80GB of Internet Explorer - Temporary Internet Files, and that seems like a lot of websites cached or something.

Please tell me whether or not I should just run the clean. It would free about a third of my total used space, 931GB, 349 used, 152 to clean, which would leave like 200GB used.

What operating system are you using?

Do you have Adobe After Effects installed?

http://helpx.adobe.com/after-effects/using/memory-storage1.html#purging_memory_ram

You can configure Internet Explorer to delete all the folders with the temporary internet files when the browser is closed. (Internet options > advanced > ..........).