In the Book of Mirrors for White Wolf, they mentioned an alternate version of XP. You give each player a whackload of XP. They decide when to use it, where to use it, how to use it. But that's all the XP they ever get. The characters develop up to that maximum point when they wish, or never spend the XP, or spend it all before even the first session. That's it, that's all.
If the 'scale' of the campaign gets kicked up a notch, the GM may give another whack of XP. So, in nWoD, the first campaign may be 100 XP. The second one, where the PCs leave the city and wind up dealing with a larger threat, they may get another 100 XP. In D&D, you might do the first campaign at a fixed 5th level, and the second one might be 10th level. One player may make the character 5th level, while another may only make the character 1st level, and progress as he sees what's needed in the campaign. It's up to the players.