I think most of the reasons are already stated. The first time i started reefing was five years ago, and what did i know then? just a 2ft tank with those cheap $30 overflow filter and a sanders skimmer and the result: crash n burn. I quit after 6 months due to other commitments, but here i am starting all over again. I have to admit the initial start up cost is tremendous, but the satisfaction from it is priceless.