late really sum it up. Nevertheless, since you're reading this column, and not touring or pleasure ride, I'd reccommend that you get one. To me, the two most important data I need are HR and cadence. I don't compete anymore, but I still wear the chest transmitter on most rides, even on touring trip. After the HR and the cadence, then it's speed and trip meter.
"there is a medical exam you can take to determine your max HR, but for most of us we use the 220-age = max HR. i'm 27 years old so my HR is 220-27 = 193. it's not perfect but it's in the ball park."
BTW It's not in the ball park, but a safe starting point for somone who hasn't taken max HR test under medical supervision. I'm not in shape competition wise, yet my max HR is over 10 beats above the 220-age. Imagine the max HR of Lance. Testing for max HR without medical supervision can be fatal.