Well, that depends on what you're using it for. It's great for taking paint off metal, removing stickers from glass, and it has been known to kill squirrels and raccoons...:laughing:
Yes, SeaFoam is a great product, particularly for gas engines that you don't run very often (mowers, generators, gas trimmers, gas blowers, etc.) I put a few ounces of SeaFoam in the tank of my Honda VTX before I stop riding in the winter and let it run through a bit. That, plus a battery tender, and I haven't had a problem. I also put in in the tank of my generator and mower. It generally keeps the gas from "going bad." It's also good for older engines. Keeps things from getting gummed up, and can clean things out if you've let an engine set for a with with gas in a carburetor.
Not sure if it's necessary for a new car engine, but it couldn't hurt. There are other comparable products as well (AmsOil makes fuel additive).