Useful for, what it's useful for.
Last week I dug out a near 20 year old consumer chainsaw that didn't run, didn't even cough or pop. Bought it 5 years ago for $5, like new but it didn't run when I tried it then, never got back to it.
Drained the old mix, put in fresh e-free/Stihl Platinum mix, nothing.
Put in SeaFoam, primed and pulled a bit to get it into the carb, and let it sit overnight. (Just didn't have time to deal with it at the moment.) Drained Seafoam out the day after next, put in my mix, and it ran. Just like that. It still has issues- not sure if it's leaking air into a cracked primer bulb or old fuel line, or maybe it still needs the carb to be rebuilt. But the difference was there, immediate, and if not amazing, definite.