Wait Mode skill tree appeals to a Tactician whereas Active Mode appeals to a Strategist and the benefit of spending AP in WAIT MODE is great should you find more comfort in a tactical role.
The AP in wait mode is designed to give players the same scope of information afforded in Active Mode, standing still.
For example, on PS4 Libra is activated with R1 (RB in XBOX), but you have to select the target and you typically only have a brief moment you can check Libra during combat. In WAIT MODE, you can be more precise in your actions because you have time to plan while you do not move.
As long as you don't plan on playing in Wait Mode, you're fine without using AP in the skills. If you do plan on it at some point however, Wait Mode is weakened unless you use the AP. Fortunately, the AP required is minimal compared to other skill trees.