I shamelessly use concurrency in Bash shells but typically I do it because I already have a Bash shell and it's now outgrowing its purpose and becoming to slow (say because I begin to use on too much data).

So instead of rewriting everything to another language, I add concurrency to that already existing shell scripts.

xargs / max args / forking to "bash -c" etc.

It's tricky. There are gotchas (with piping for example but also how to behave when one subshell fails, how to cleanly interrupt everything if one fails, etc.).

But it works and it's a cheap way to greatly speed things up.

Also that's the kind of stuff that became not just a bit but much easier now: just give a shell script to a LLM and ask it to add concurrency where needed.