The next version of Mastodon can't come soon enough.

About 20GB of disk space on my instance are being taken up by media from remote users. And this is for a single user instance! I can't imagine how it must be on other instances with multiple accounts.

A recent PR should make things much better though by allowing you to remove these files.

The only thing you need to do is pass the --prune-profiles flag to the media remove CLI command.

The PR is already merged so hopefully that means it's coming the next release.