It changes the viscosity of the oil. Plus you don't want all the sludge it busted loose floating around in your engine, looking for something to clog up.
I wouldn't get too carried away putting it in the intake too often. Just add it, or any good fuel injector/intake cleaner to the tank every once in a while after you've done the intake treatment a couple of times. If you need it more than that, find out when you have oil geting into the intake.

 

Its a solvent.... of sorts. Probably breaks down the oil, as well as cleaning up some of the crap that accumulates in the crankcase. Don't wanna leave that stuff in there, so, changing the oil cleans the seafoam, and whatever crap it broke loose, out.

 

I see. Well I will added one bottle last week. I plan on heading to the store tomorrow so I will get a second bottle and add that, then change oil this weekend.