I've accidentally pruned some remote branches and I don't really know what the consequence of this is (I clicked the "Prune remote branches" button in Git Extensions, thinking it would delete a remote branch).
The official documentation says "git-prune - Prune all unreachable objects from the object database ". I don't really understand what this means. I'm guessing this might have removed merged branches but I'm not really sure.
Answer
"Prune remote branches" in Git Extensions executes git remote prune command, which removes your local remote tracking branches where the branch no longer exists on the remote.
See here: https://git-scm.com/docs/git-remote#Documentation/git-remote.txt-empruneem