So, once you learn a vi command, you can use it with all the motions you already know, and once you learn a motion, you can use it with all the commands you already know.

The other aspect, that is more insidiously useful: vi is almost everywhere, and will easily fit on an embedded system. It's a rare server that doesn't have it, either. This is definitely vi, not vim, when I say this, though.

Command mode lets you manipulate text using a full keyboard as shortcuts. Depending on setup this can reduce the amount of chording you do.

Visual mode lets you select text. By character, line, or region/block. I find this easier than emacs selection.

Insert mode what you use to enter text.

After a few weeks of fighting it, I switched to evil-mode emacs and was pretty happy since then.

I have been using a jetbrain IDE recently and surprisingly, the vim plugin is pretty decent. So knowing vim lets me use both the IDE and emacs with less friction.