Cadence sensors are good for teaching you how to adjust cadence sensors. Seems most of the folks I ride with are constantly wrestling with their cadence sensor trying to get it to pick up. T he things seem pretty finicky.

I have a Shimano flightdeck computer with virtual cadence. I like having cadence info available, and I think it's really useful for new riders. Like others have said, on the flats try to keep your cadence above 80. On the hills just try to keep your legs from burning to a crisp and your heart from ripping out of your chest and turn whatever revs you can.