An emcee (MC) is a critical element of any organized event. Some folks have the skillset to do it themselves, but most people will find that they need someone to address the crowd, control the flow of events, maintain a certain energy and generally guide the party in a meaningful direction.
A good emcee can add fun and excitement to the party simply by the manner in his/her voice and some useful tricks-of-the-trade. Or (s)he can create a warm/emotional moment when that is appropriate.
This does not mean talking constantly, or hooping and hollering all night. I learned from some of the best guys in the industry, and their advice was simple: “less is more”. That means make the announcements you need crisply and succinctly, take assertive control on the mic whenever it’s necessary, identify the moments where a comment will add energy/life to the party… and then shut the hell up the rest of the time.
A big part of it is the confidence of having spoken in front of large audiences enough to know you’re doing the right things right. You don’t have to be the center of attention, nor do you want to be some kind of superstar… but there’s a job to do so get it done and then let the folks enjoy themselves.