@Coin missed my perfectly valid point, obviously.
If video games today - such as AC - had no discreet method of saving progress, like games were in the arcade oh so many years ago, fueled by nothing but coins, much of the most popular games, most laden with story formats, would not be so popular.
The average player does not wish to start in the tutorial every time they sit down to play a game that has a form of progress. Nobody wants to start each AC game in the tutorial, every single time they play, no matter what you say. There is far too much exploration, map opening, far too many puzzles, far too much currency management, equipment upgrading, and so forth, that goes into most AC stories, for you to turn the game off and start in the tutorial in the morning, hoping to beat your record time to the place you left off before lunch. Worse, is if you had a random power outage, or someone who kicked the cord out, after you just spent the morning getting to where you were last night, and oh yay, you get to start in the tutorial again, sux to be u.
If you did have to beat yourself to get to where you were, every time you played, AC would not have the popularity it holds tonight, because finishing a story like that is too complicated in such a system with no saved progress.
It is different when you are playing basketball in the driveway and start at no points, but for the record I also don't see anyone mid game saying we should reset the points to zero just cuz it'll be funner if we do.
Most people like to have a way to preserve progress in anything they do. We like to have a place to pause. Yes, sometimes you want to grind out that old game, dusting it off and putting it in, starting without a saved game, but this is why we call that nostalgia. I don't see anyone complaining about how unfair it is they get to save so often. I also don't see most painters complaining when they reuse an old canvas as opposed to spending a few days mounting a fresh one every time they get the urge to do some painting. As human beings, we like the convenience of our conveniences.
Next time you want to try out how fun it is to start at 0, go to a hockey game and suggest at the half that they start with 0 after some goals were scored. See where you get. I'm betting they would look at you like you were a fool.
I stand by my statement: You could earn a rollover. You could save one up, and use it when you think it is appropriate, but you could also have a few enough rollovers available, that you have to make hard choices between when you want to start over completely, and when you want to not start over. Just having some sort of option available is something nobody is going to ultimately turn up their nose at, even if they never use it. It's just nice to have it available.
This is doubly so in a MU* environment. It is just nice not to start over when where you are headed is peopled by friends who are so much more advanced than you are.