If one is capturing and clarifying absolutely everything potentially meaningful in one's life per DA's recommendation, the problem with organizing by AOF is that you'll have to constantly be reviewing actions you can't do when and where you are. That creates resistance to using one's lists. That's not dogma speaking, that's my personal experience. If someone wants to manage actions using a top-down approach, I don't think it makes much sense to practice GTD which is at its core a bottom-up approach. It might make more sense to try something like Franklin-Covey or one of the other more traditional approaches.