It depends what you are willing to spend. A good emcee can usher and set the mood. But if you think about it another way, you are really paying thousands for someone to just speak for 20mins on stage.

When I did my wedding dinner, thankfully I had someone who was willing to be the emcee, that really save me thousands in another vendor payment.

Not definitely need. like i said...if you engage one, you are paying few thoursand for sometime who only speak for 15mins