The reason you can walk into any Sams Club and get free samples is because they know people are more inclined to buy after they try. It costs them to provide free food, but it doesn't cost the artist to supply a limited number of bits and bytes.

Consider Lindsey Stirling's dubstep video that is freely available on Youtube and has gotten over 27 million hits.... the free exposure has surely sold a lot of her music.

Naturally, if your music sucks making more people aware that it sucks won't help you sell it. But if it is really compelling... and if people have an easy and free way to hear it.. I would think that would work to the artist's advantage.