MonstroMart:

I assume some space reserved for swap files and caches (shaders, ...). Probably some place reserved for temporary download. Some place reserved for future update. Steam itself, the OS itself, maybe Java in case there's some java games/apps on the store i would be surprised if java is not installed, not sure how Proton works but i guess it involve some kind of windows files or image or something? I highly doubt Proton takes less than 1GB i think Wine takes 1.5GB minimum or something like that. I would not be surprised if Proton takes close to 2GB. From what i've seen it's quite good. Maybe Source is pre-installed.

It should have enough RAM to not need a swap; Unlike Windows, Linux by default doesn't use swap unless you're running too low. I thought of the temporary download space, but, Steam I think downloads and decompresses the files on-the-fly, and it checks how much space you have left before you begin a download, so I don't see why it would need to do that. If there are any games that use Java (not sure if there are any), they would be packaged with a JRE. Same goes for Flash games. Yeah, Proton uses about 1.5GB. Though, I guess where it really starts to take up more space is when you have multiple versions, as some games only work with a specific version. So, having a few versions installed would rack up some of the space used rather quickly. I don't see why Source would be installed, but who knows, Valve might have their own reasons for putting it in there.

Y'all seem to forget it's 2021 and 10GB is like nothing nowadays 😉.

Not when you've got a 64GB drive and when a single game can often be triple that. There's no need to needlessly waste disk space. That isn't to say Valve is wasting it, but, they apparently have cleaned up a lot already.

Pretty amazing that they have got thousands of windows games working on linux to be fair. Makes you wonder what native linux could do if developers werent tied to a resource hogging OS right now