Mastering is the final creative step in audio production—the last chance to enhance sound or address problems before replication.
Technically, mastering readies your mix for smooth playback across playback systems. Numerous enhancements and alterations can be made such as analog sweetening or mix repair.
Mastering ensures your final tracks have balance, separation, flow, and consistent loudness. Simply put, a proper master will ensure that your music will sound its best.