Hiring someone who has experience will definitely help your stress level both before and during the wedding. A experienced professional will always have their own way of doing things taking the guesswork away from you, leaving you to enjoy your wedding.
As a professional photographer I have spent thousands of hours photographing weddings. I know when that blissful smile will all of a sudden appear on the bride's face and I'm always ready with the camera. That loving look on the groom's face, which is always in poor lightening can and must be captured and a true professional is always right there, ready for it.
Remember the food and flowers will become a faint memory but your wedding photographs are forever.