Well, here is my reasoning...
If I am not mistaken, expeRience in both AW and DW is solely accumulated to gain an Advance or a Level Up. There are no ways to spend it during active play to do anything else.
On the contrary in FW you can first and foremost spend 2 expeDience to gain 1 Advantage (also multiple times, to offset Disadvantage) in any roll. Another use of expeDience is to fuel some Common and Class moves, . In both cases these points are very convenient to have and use, and mainly boost a PC's efficiency/effectiveness.
Then, if you amass a lot of them, you can spend them to speed up your personal Growth.
Does it makes sense? :)