In music they are a way to create buzz on a otherwise unknown track. More recently it has been used to help music have crossover appeal. In particular hip hop/urban music makes their living from this method. Recently I discovered a collaboration between meek millz and Dave patten. The song worked well because their voices are of different quality and are in harmony. For us at borindom we are currently working on a track(lyrics/production) to be sold for that purpose.
