Heart rate, for one thing. Which is more important: AVERAGE HR, or MAX HR? Or does it depend on what kind of workout I'm doing?
Average and max speeds were data my Cateye Strada gave me, so I had been tracking that for several years. (I might still be using that Cateye, but it wasn't working well. I figured it was wearing out). The Cateye of course recorded distance and ride time.
But it didn't tell me how many calories I had burned during a ride. The Garmin does. I have to plug the Garmin into my laptop and enter some personal data, including my weight. The Garmin does the calculating on each ride.
I've barely begun trying to enter ride routes. I need to learn, though, if I want to do long rides in unfamiliar territory and not get lost. Funny story: many years ago my mother mentioned a bumper sticker she'd seen on a neighbor's pick-up truck. At the time, this man was training bloodhounds, and the sticker said: "Support Your Local Bloodhound. Get Lost!"