As others have said comments are currently not purged. I think they are deleted only if you delete your account. So, if you are really into it, you could apply that as a periodic solution, but it would nuke everything and not just some parts.
In theory, if I understood correctly, you can overwrite your comments and only the new version should be kept in the DB and propagated around the other intances.
So, potentially, you could substitute a really long 10k words essay with a 2 words comment, but personally I don’t see that as a viable “saving space” effort. We are talking about a relatively really small amount of text and space on the grand scheme of things.
I’m unsure about the keyboard but the caps are from the Drop + The Lord of the Rings MT3 Elvish Keycap Set