When I say Mobile, I mean things you have to not stop and cast....
For example Wardens ...They have Mobile Cone Effects so you can run a bunch of them and just run around in a zerg of them hitting the cone aoes over and over.
a Non Mobile Cone would require you to stop in place to cast it.....
What does that do? It makes your groups far more easy to be hit by opposing AOE and such.
Steel Tornado would be an example of a Mobile PBAE you just bloody spam...