This is something I have always wondered about.

Though learning how to use the debugger is a good skill to learn, these days I don't know anyone around me who has ever used a debugger, or even finds a use for it. I think the best tools of our age are really REPL's, which allows you to test out your guesses/hypothesis in the form of snippets.

Personally I have probably used a debugger 5-6 times in my whole programming career, these days I hardly find a use for it.

On the other hand, I find tools like these very useful: https://metacpan.org/module/Devel::NYTProf