Having a photographer for an event that you are planning is a nice touch and in the long run, it is one less stress you have to deal with.  Having hosted parties myself, I know that with so much going on, you finish up the party and then realize that you wish you had gotten a photo of something special but your mind with running in every direction that you forgot to get that one photo.  As an event photographer, I am there to photograph the entire event and capture all those details while you are busy relaxing.