That's a good question. I think this used to be the standard but folks are chilling out now. Probably for a lake where ther are a lot of skiers waiting, you still need to maintain a limit, but all of the places I've skied recently just tell you to go to your heart's content.
However, I do find that even at the peak of my (short) season, there is a point where any extra passes are not doing me any good, but rather the opposite. Folks I ski with all agree that as you body gets tired, you unconsiously take a diferent, more defensive body position and then frustration sets in and you decline. So less can definitely be more, especially in this sport.