Think of it like weightlifting:

1) Lower reps, higher weight to BUILD muscle, comparable to mashing at low RPM in a high gear
2) Higher reps, lower weight to TONE muscle, comparable to spinning high RPM in a low gear

A higher cadence has lots of other benefits; most notably (to me, at least) less muscle fatigue. I've been working continuously to get my cadence higher. I'm usually spinning in upper-90s to lower-100s.