Nice article called "Where To Not Cut Corners When Planning Your Wedding." Wedding planners and coordinators definitely made the list! See #7!
"What you can expect from this coordinator is someone that will start working with you 2 months prior to your wedding date when things really get busy. The coordinator will design a timeline with all of your vendors from beginning to end to make sure that everything stays on time. The coordinator will also be on site, typically with an assistant, for the entire day to make sure that they are there to handle any problems that come up."
Sure, you might be super close with someone that has DJ'd a few parties, and maybe you do like the idea of your cousin as your officiant. Trust us, keep your friends and family as guests at your wedding and not as vendors....