The only advantage that I see with a pre rope drop ADR at AK is that you eat while the park isn't open as opposed to spending time eating while it is open. Other than that, there isn't much of an advantage to doing it vs just arriving at the rope drop. AK is a 1 day park and outside of Expedition Everest, nothing is worth doing more than once (although Primeval Whirl is a lot of fun) and arriving at the RD should allow you to experience everything you want to experience there.