I think it's all moot and similar to the question of "How much should you risk?" Well, it depends on how sure you are. If you are quite sure, you should go max leverage every trade. If not, smaller, and incrementally.
I can see scaling out for profit (dependent upon position sizing and target range) but I am a strong believer in taking a loss at once and in its' entirety once the stop-loss level is reached. Just my own 2 cents, YMMV.