I've lived all of my 34 years in and around saltwater. I have used aluminum boats in salt the entire time and have never put one on an aluminum boat. I'm NOT saying don't do it. ANYTHING you can do to preserve your boat is worth it or if it gives you peace of mind. IMO if your going to leave your boat in the water, please add one if not buy a device that is an electrical anti-electrolysis device (expencive but the best prevention for boats staying in the water). I use my boats every weekend in saltwater and I just hose it down and flush the motor after each use. Most severe electrolysis is caused by stray voltage from your electrical system or some power source in or near the water. A battery grounded to a aluminum hull that sits in saltwater will eat aluminum like a ice cream at an 8 year olds birthday party. I always unhook my batteries after each use or turn the battery switch off.
Hope this helps. If you want more info. Google boat electrolysis and there is tons of info. and devices to fight it. I wouldn't fret about it as long as you soak your boat for several minutes. I always wet the entire boat first to disolve all the salt. Then I go back and hose it down. I am having problems with my TM but it is my fault. It is a freshwater TM.