I have Auto-update filter lists on. Under Dashboard/3rdparty filters there's a Purge all caches button. If I click it the filters become outdated, and when I update the filters the purge cache option reappears. So... I don't get it, should you use the purge function or not?
No, see this thread: https://www.wilderssecurity.com/threads/ublock-a-lean-and-fast-blocker.365273/page-40#post-2483161 Especially post 993 and 997