It's pretty much a case by case basis.
Character A can make a storm, and make full use of the storm to attack.
Character B can make a storm, but only ever uses it as a stockpile for his attacks, e.g. 1 lightning bolt at a time, or a gust of wind, etc.
The difference between them is that while they are both capable of let's say, 7-A storm creation, one can use it fully while one can't for some reason, which is a limiting factor to their AP.
It's hard to explain but the best I can think of is Emiya Shirou.
(Spoilers abound for anyone not caught up with Fate)
Teen!Shirou in UBW series was able to create Kanshou and Bakuya strong enough to hold off Kuzuki, who was strong enough to toss around Saber, but he leaked a lot of energy when creating it, shown by the amounts of arcing lightning and whatever effects were happening on creation.
Adult!Shirou in UBW series was able to create Kanshou and Bakuya the same as Teen!Shirou, but he doesn't leak as much energy during creation evident with the effects being barely any motes of light.
If both Teen!Shirou and Adult!Shirou used the same ability to summon the same weapon with the same amount of energy, but Teen!Shirou wastes a lot of the energy in the process, then Adult!Shirou will have more energy packed in the weapon, thus being stronger, evident in their eventual clash where
Teen!Shirou's weapons were getting broken faster.
TL;DR, control is imo, another factor of AP. Not just capacity to release power.