Well IIRC in games like the classic Dragon Warrior/Quest 3, that was one of the first games where you could change classes for all your characters except the hero. It was good for rounding out a character's attributes and giving them some diversity in skills. You'd have to stick with it awhile before you could change again.
This would greatly affect stats and skills you could learn.
Personally I think it's okay. Like if you became a soldier but later decided to become a smuggler. However I think there might be some drawbacks to crossing classes. I.E. You start off a consular and evolve to sage, but you change to the more combat oriented shadow and you'd only have rudimentary and intermediate force power skills from previous while now you could only learn one additional lightsaber form as opposed to two or three, and you may not have any choice which one.