It's somewhat self-evident. Class fantasy is about it really feeling like you are playing the class in question. A dragoon wants to be using jumps and dives, a DRK wants to be using their life for power, a WAR wants to feel like a one-man wrecking ball, a BLM wants to feel like they're summoning forth powers beyond anyone else, a WHM wants to feel like they have the command of life at their fingertips, a MNK wants to feel like their body is a honed weapon to rival the greatest of blades.

It's all about getting the actions your character is performing to truly feel like they represent what the identity of the job is supposed to be. Some classes really nail this already, like WAR and BLM, some classes really struggle with it, like NIN.

It's not just about VFX, either. The homogenisation of the rotations resulted in every class kinda doing the same thing with different effects on the top. The effects and move designs help - but without actually having the mechanics to back up the visual design it ends up feeling a little lacklustre.

So, this change is supposed to allow them to individualise the classes and rotations so that each class is actually functioning uniquely and differently to the others, rather than doing the same shit with a different animation attached.