Dermpath fellowship spots are rolling. I luckily had an easy time with it and my first offer was at the program where I wanted to train. However, experiencing both methods, the match (vs rolling offers) is much better (and organized)....and this is coming from someone who didn't match Derm first time around in the traditional match.
Stop and think about how a rolling process works. If you get an interview offer from shabby program A, you take it...it's an interview and WHO KNOWS WHAT WILL HAPPEN (if other programs would even offer you an interview). The place calls you a week later and offers you a spot. You can't just sit on it and collect offers. You're supposed to get back to them within a few days (enough time to discuss with family/sig others, think about location, etc). You then decide to take the spot because WHO KNOWS WHAT WILL HAPPEN (if other programs would even offer you an interview, let alone offer you a spot).
Your options would have been:
A. Play it conservative, take the spot, get no more offers, thank your lucky stars
B. Play it conservative, take the spot, super dream awesome program offers you an interview a week later...but you already accepted what is to be assumed a binding agreement (that's a whole potential Pandora's box right there).
C. Risk it, turn down the spot, get an interview from awesome program. But don't get an offer. Sorry!
D. Risk it, turn down the spot, get an interview from awesome program. You are offered a spot...BINGO, winner winner chicken dinner.
E. Risk it, turn down the spot, get no other offers. Sorry!
That's a simplified example and there may be other scenarios I'm missing, but as you can see, only 2/5 of those scenarios are optimal outcomes.
Hopefully that illustrates how a rolling process puts the power in the hands of the programs.
That doesn't even get at the fact that in a rolling offer system, programs would all front load their interview schedules to try to get the best candidates. There would be tons of scheduling conflicts, missed opportunities, wasted time, crossed wires, etc.