Since adopting TDD, my debugger use has really dropped off. I think it's partially due to TDD encouraging me to develop more pure functions and push side effects to injectable (and thus mockable) objects.

But every so often I encounter a state that I can't understand how the code gets into, and in those cases being able to step through everything that's going on is incredibly helpful.

I may not use my debugger every day, but when I want it, I'm sure glad it's there.