Oooooo! It really depends on whether someone is late or call in sick. In fact the very next day I had another airport reserve and I actually got called to do a trip because a flight attendant was running late. At first they just needed me to board passengers until she got there, but she ended up not showing so I worked the trip.
Being "on reserve" you really don't have a say in your schedule. You go where they need you and that's it. "Lineholders" have a little more control over their schedule and EVERYTHING is based on seniority.
