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.

PCussy

It is probably an old case design. In the early water cooling days, there would be separate watercooling units that sat outside the case. The grommets were so you could pass your tubing through.

I wouldn't really worry about the dust tbh, you will wind up having to clean it regardless.

Hole for Pepnis

( ͡° ͜ʖ ͡°)

Just leave them be. I think their point was to route tubing for custom water cooling loops.

FYI this community is meant for open-ended questions.

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.

Dust will get in pretty much no matter what you do. I wouldn't worry about it. If you live in an already really dusty environment then get some sections of filter and attach them inside of these holes but honestly I wouldn't worry.

It's for water cooling loops if you want to mount the rad or pump or something outside of the case. I think it was more common in the early days of water cooling when things were less standardized.

We have the same case! Twinsies!!

Watercooling holes. That said, I've never seen anyone use them. Mounting external rads is a bitch. They take up space. Most people just buy a watercooling compatible case.

Those are for your watering system

They're like buttholes for your computer

Those are rubber grommets. They'll protect cables from wearing on metal that pass through the case.

Likely for things with hard wired controllers, like fan controllers or led lighting. You can hang the controller outside of the case in the back where nobody will see it.

Besides the water cooling that's already mentioned, those could be used for example for routing an internal device out and into the I/O of the motherboard. An example would be some fan/RGB controllers that are meant to be somewhere inside the case, but are terminated with a standard USB A plug (and very few motherboards have that as an internal connector). Another example is a mini display that you could put inside the case that would need to interface with the GPU (so you'd need to route a DP or HDMI cable out of the case and into the back of the GPU).

Is that an NZXT? It looks almost exactly like my old case I just repurposed. (And yes, it's for water cooling but those cases have exceptional air cooling so it was never that important.)

Those look like optional expansion ports cut into the case that were filled with plugs because the configuration didn't need them. The shape I'd really odd though since the only thing that comes to mind is that they were intended for additional power cables - the shape is weird.

Edit: Downvotes for attempting to answer the question... awesome.