Most of them come from you browsing the internet. There are also system temporary files. Keeping these deleted makes your system run faster.
Wouldn't temp Internet files be in their own folder? I just thought it was weird that these temporary files were actually also system files....maybe I should try to locate them before deleting them.
Temporary files are created by programs and Windows itself. They store data while the running session is active. They are then no longer needed by the program and are marked for deletion, though Windows nor the program deletes them on their own. Don't waste time trying to locate them before running a cleaner.