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.
They are external ports for water cooling. They allow you to run the pipes to an exterior location, and I have never seen anyone use them ever. I would leave the rubber grommet as it generally looks nicer than the hole.
The rubber didn't agree well on my old case. I poked it a couple years ago trying to figure it what it might be and the little triangles has gotten stiff and snapped off on one side, so I stopped poking it.
I was today years old when I learned what they were for though. I knew it was some kind of tube or pipe or hose, but I've spent about 0.3 seconds actually thinking about it so I never figured it out.