basically, when you use a dress sphere, its like a job. You use the job more, you gain more skills in that job. So in a way you can have the customization since you can choose (as opposed to the game automatically choosing) the skill you want to learn next.
the sphere grid is nonexistant though, which I think makes the game a bit easier ( Final Fantasy 10 didnt give you enough exp and spheres to properly traverse the grid in my opinion )