Kristian Dowling, Getty ImagesIn hip-hop, the guest feature can serve a wide variety of purposes and often many simultaneously.There are times when the host rapper is playing armchair A&R with the goal of putting on a close friend who typically has few songs to his or her name. Other times, the complete opposite occurs -- some unknown comes on the scene with a verse or chorus from a buzzing or high-profile artist. There is also the posse cut, wherein an MC gathers everyone he or she can to contribute to (usually) a remix that gets decent radio play or Internet attention and then...…Kristian Dowling, Getty ImagesIn hip-hop, the guest feature can serve a wide variety of purposes and often many simultaneously.There are times when the host rapper is playing armchair A&R with the goal of putting on a close friend who typically has few songs to his or her name. Other times, the complete opposite occurs -- some unknown comes on the scene with a verse or chorus from a buzzing or high-profile artist. There is also the posse cut, wherein an MC gathers everyone he or she can to contribute to (usually) a remix that gets decent radio play or Internet attention and then...WW…