It really all comes down to what you want in your tank. If your goal is to get the pastel sticks of acropora and have a totally algae free, ultra low nutrient tank, a skimmer will probably be part of your toolkit. If you're just going to have zoas, and other soft corals, skimmer isn't as much of a necessity. I certainly won't make the claim that it's a necessity, I just view it as another piece of the puzzle for me. Other methods to get you where you need to go are, biopellets, macroalgae, carbon dosing, low stocking, large water changes, deep sand beds, etc. Anyone who uses a single one of these as a panacea is probably in for a bad time.