Just now, HappyDaze said:Not all players are going to want to predetermine what their character's emotional strength(s) and weakness(es) are going to be before the character even seen play. They would prefer to roleplay without such rails laid down beforehand and see what comes about as the character grows. You even mention that you do this yourself when you say, "I don't use it, personally, since I prefer to let the story I have in mind tell itself," so you have at least some agreement with the idea. If you take out the strengths & weaknesses, then Morality becomes just a measure of light vs. dark, and while it could be fine like that, it is far less interesting than Obligation (I don't much care for Duty myself, so I'm only going to discuss Obligation) in play.
Strength and Weakness aren't the only personality traits a character has, or even necessarily their most obvious ones. They're just the ones most at the core of the character, which I daresay any experienced roleplayer has already figured out, or at least has an idea about, before starting. It's not rails, in that the character can't act out of other personality traits, or that the character must act out of these ones all the time. And for inexperienced roleplayers, having handy little adjectives to describe their character can help them slip into that altered frame of mind.