Seafoaming is good idea when your car gets up in mileage and age...
What happens basically is that you have what is called an EGR system on your engine which recycles spent exhaust gases back thru the engine...What that does is cause carbon buildup on the internals of the engine over time...Over the years it gets caked on...Good for emissions but not to good for your engine..
Basically the seafoam disolves all the years of carbon buildup in your combustion chambers and throws it right out thru the exhaust... That is why you get the tremendous smoke clouds when seafoaming your engine...
Some people have seen as much as 10hp gains when seafoaming, but it should make the car run a bit smoother as well...
It's a good idea to do it with cars over 50,000 miles or so in my humble opinion... Just make sure when and if you seafoam your car to warn your neighbors or do it in a very open area...The fire departement may just show up...
You can purchase Seafoam at most auto parts stores or I bought mine on Amazon.com...