As an MC, it is the performer’s job to warm up the audience, introduce acts or speakers and provide a bit of magical entertainment or comic relief to keep an event moving along.  He fills gaps, or dead time, while the stage is being changed or other things are going on behind the scenes.  He provides a touch of professionalism, so the event organizers can concentrate on what they need to do to get their message across.  Use an MC when you have program of different speakers or acts and need someone to tie things together.