What forms the emulsion in chocolate?
Chocolate consists of tiny clumps of cocoa solids, sugar, and milk solids dispersed in cocoa butter.  Because the solids aren't soluble in the butter, they tend to clump up, which reduces the quality of the texture of the chocolate, it feels less "smooth."  When you add an emulsifier, the hydrophilic end tends to stick to the relatively more polar surface of the solids (the proteins in the cocoa solids, for example, or the carbohydrates) and then the hydrophobic end interacts favorably with the cocoa butter.  The coating of emulsifier tends to help the clumps stay small and well dispersed in the fat.  That makes it easier and faster to process the chocolate, and it also lets the chocolate last longer before the fat and chocolate solids start to phase separate on a macroscopic scale.