You don't have to have GPS on your fish finder, but for the little extra cost of having a dual unit. You end up having a back up unit if one of the others fail. No matter how good you are at navigating out on erie, if something happens to you while your out. And you have your GPS set up properly so anyone will be able to read it, you/they have a chance of getting back to port. As far as side scan, for me I dont' find where I even want it. I've seen it used and do not find it an added feature for me. It's like everything else, a personal preference.