VI is always available and will run on the most crippled, single user mode, broken graphics, no keymap, slow link machine - so it's worth knowing how to edit simple files in it just for sysadmin tasks.
Emacs is a complete user interface in an editor. The idea is that you fire up Emacs when you start the machine and never leave it. It's possible to have thousands of sessions present.
Whether learning the capabilities of Emacs are worth it compared to using a GUI editor/IDE and using something like python/awk/etc for extra tasks is up to you.