I'm coming from a fitbit and on that, I'd just choose "workout" which would track my heart-rate and calculate calories burned. Wasn't super precise, but I know what I do at the gym anyway, I just wanted to keep track of time I was active.
Having to put in my workouts really hinders my flow, as well as the fact that sometimes, machines aren't available, etc.
Additionally, I'd choose the same thing when I play soccer or ultimate frisbee. It would just track steps and time and calculate calories. I can't figure out any way to do that for my new Garmin. I guess I could put it in as a run, but I'm not trying to keep track of pace or distance, just steps and vigor.