I put one ounce per gallon in my VS650 when I know it will not be ridden for a month or more, usually this is only during the winter.
I also use it like carb/injector clearer on any motor vehicle or the lawn mower when they seem to be not running right. Since it has a shelf life of about one year, and the Vstar only needs 4 ounces out of the 16 ounce bottle, it gets used up in one vehicle or the other within a year.
I get the sense my bike in the spring seems a bit off on that tank of gas with the seafoam from last december. It does keep the gas from degrading, but Im not sure if it also throws the engine or ECM off just a bit when you use it. Even with a fuel stabilizer old gas is still old gas.
I have also put it in the crankcase about 500 miles before an oil change a few times, once on my Vstar, and once in a car that burns a lot of oil. Dont know if that accomplished anything.
I have never heard of seafoam harming anything.