I use them to quickly learn new languages or libraries. E.g., I’ve done only C++ for a few years and got rusty in other things. I used copilot to quickly learn how to create a Python Flask server, how to draw shapes on an HTML canvas with JavaScript, how to write common algorithms like “generate a random number in this range” without having to reach for pen and paper, etc. all without leaving my editor. It’s kind of like a much faster Google search for a StackOverflow result, and keeps you in the flow.

Disclosure: I work at Microsoft, opinion is my own.