I didn't use any for years and things were going along just fine. I started using AA and other vitamins and after a year found very little if any difference (but I have always fed a VERY diverse mix of foods). I quit AA and vitamins for a year and again found no significant difference in health, growth or color in my sps and lps corals. I have had a very low cost supply of AA and vitamins for my tanks, so I'm using some again. But if I had to pay the going retail rates for AA and vitamins, there is no way I could justify paying that much for so little affect.
Not very scientific, just my 2 cents worth.