What are the rubber circles for on the back of my pc case? Should I just leave them like that if don't have a need for them? Or are they likely to let I'm dust into the motherboard?
Edit: thanks for all the replies, so just for water cooling I have no need for.
Well, you got the answers you were looking for, here is a different answer. To your other implied question, how to not worry about dust getting in other holes.
Main thing is to develop positive air pressure. You want more powered intake than powered exhaust.
Use fans for all your filtered air intakes, ignore powered air exhaust, run it at lower fan speeds if you can. Air will get out fine. If you force the air in where you want it to go in, dust will only go into the easily removable filters, it won't be on your components. Any extra hole in the case will just be exhausting the already filtered air. Then just remember to actually check and clean your filters. That's the hard part. But if you clean them when they need to be cleaned, you will never have to actually clean the inside or the fans or components or anything else, just the filters.