Photographer or Person Taking Photos?
In today's day and age everyone has a great camera and they can correctly use that camera to get the pictures you like. Everyone can be a photographer but you don't want to just like your photos, you want to LOVE them. If you're having your wedding photos done you don't want those photos to be just like any other picture. You want them to be original and showing your best features and interests.
Photographers make the photos, we see more than whats already there. We see angles and lighting and reasoning for everything that is in the image. While someone just taking photos sees just the subject and the pose a lot of the time. Photographers look at detail better than someone just taking photos.
Also behind the photos, most if not all photographers have experience with Photoshop or some type of photo editing site. If an armature is doing all the behind the photo work it may turn out to be too much color and it takes away from the subject, not enough and it takes away from the subject. The photo editing it a key part of making a photo.
This is why you should use a photographer over a person taking photos. They're more experienced and have a better understanding of photographer in general.