Commercials

I think people, subconsciously, generally like familiar things, and/or reversely, fear the unknown. A song not particularly to your liking will be heard hummed by you randomly after enough exposure. Having been seen at least once by an unknowing customer is an advantage to a brand when competing on equal grounds in other regards (quality, availability, even prices). Customers tend to want to feel safe when buying things, so a little extra (though probably false) sense of security is worth the decision to buy or not to buy.