I've had no trouble falling asleep quickly so there would basically be no difference. (In fact, I've experienced an opposite effect with the couple of times I've taken melatonin.)

For people who actually have trouble falling asleep, or wanting to fall asleep, this is definitely a concern. When I was researching melatonin a few years ago, one of the problems I read was that if you fight off the effects of getting sleepy long enough, you'll actually find it more difficult to sleep afterwards (that night, I mean). This was the reason I chose to avoid it after a few tests at that time: I didn't feel I could afford the risk of accidentally pushing through the sleepiness and getting almost no sleep in a given night.