I've been using DP as XP for a while, you level up at every increment of DP. (i.e. if it's 40 DP/level, you go up levels at 40/80/120/etc) and you are one level ahead of where common sense would put you. i.e. if 3rd level, including 0 level, is 4 levels, you might think it's 160-199 DP, but actually it's 120-159, since in the current system you spend all those DP the moment you hit a level, so "3rd level done" is the 160 point, not "third level starting" at the 160 point.
Level is needed just to resolve costs so if you're paying X/Y for a skill, if you purchase 1 rank at X, you have to wait to level up to purchase another rank at X, if you purchase another rank without waiting for level up, you pay Y.
It's a bit more bookeeping intensive, since you essentially have to do a mini level up after each session, and some players seem to prefer just spending it all in one chunk rather than having to fiddle around with spending (or choosing to save for something big) 5 or less DP at a time, so it's not 100% upside.