A lot of brides think they can save money by getting a friend or family member who are good with a camera to take their wedding pictures. I have also heard a lot of horror stories where a bride had horrible pictures at the end of their wedding, so all their tangible memories were lost.
Yes, I have heard horror stories from brides that hired professional photographers, but it's a lot less likely. Professional wedding photographers have worked a ton of weddings and know what important events need to be captured on camera. They also know how to deal with big groups of people.
When looking for a professional photographer, make sure to look at their portfolio. Also, make sure to ask them a lot of questions to make sure you're compatible and that they will give you fantastic pictures.
Even if you hire a professional photographer, you can get your wanna be photographer friends and family to take pictures as well. That way you have the gorgeous pictures from your photographer, you'll also have great candids from friends and family. Those pictures will catch things that your photographer didn't see.
Final thoughts: A photographer is a need!