In case you need to remove a tag from your Git repo. Local and remote.
When you need to remove your last pushed commit.
If you're a member of different development teams or you have a multiple GIT remotes setup, you might need to deal with multiple SSH identities. In my own case, I use my own git server (with Gogs) and BitBucket for my private repos, as well as GitHub for my public repos and gists. This is my setup to deal with multiple SSH identities in OSX.