I found it useful to learn just because there's so much existing code that's been written in it.

Means I can at least dig through some old codebases and understand what's going on.

Lots of higher level languages also have C bindings, so at least a couple of times in my career I've ended up writing short C modules for speed critical bits of code.

The pain of manual memory management also gave me much more of an appreciation of its pitfalls and alternatives.