Have you ever gone through the hassle of having multiple public/private keys for accessing your remote servers? Before recently, I used to specify the identity file in all my transactions `ssh -I ~/.ssh/private_key user@host` but no longer! I discovered you can add the following to your `~/.ssh/config` to specify which key you want to use!
Of course you can add multiple of these entries in that file so that you can `ssh` without having to worry about explicitly using keys. Just keep in mind that the order of your entries matter.