So I am not an expert in this by any means, but if I understand it, Gen2 (R55/56) MINIs get carbon buildup in the engine. Seafoam, when applied like this, soaks into the carbon buildup, loosening it, and letting it be cleaned out of the engine.
Someone else please correct me if I am wrong.
I think that I have heard that once every 6 months or so is helpful.