All this bpm talk is cramping my style. Playing scales on the piano I had to use a metronome because it was classical and precision is key. I guess the same thing stands for classical guitar and a certain kind of rock is classical based so that's why a lot of guitarists use one. If you ask me, though, it's not an absolute necessity. If fact, I'd even blame it on the downfall of rock and roll.
Too much attention to precision and speed and not enough on creativity is why the 80s sucked in my opinion. What style of guitar playing dominated the 80s - classical. How do you practice classical - with a metronome. You kids can play fast and precise but what else can you do.
Make boring tunes.