When a couple asks me if I shoot with 2 photographers or 1? That is an easy question...I just shoot with 1 photographer.
I find that I capture lots and lots of photos that gives a bride and groom with a couple hundred of photos to pick from. A second shooter is unnecessary.
Here's a little example well the perfect example I think of why you don't need 2 photographers. Think of it this way...If you were to have 2 hairstylist they would get in each others way, fighting and pulling at your hair. You wouldn't want two hair stylists fighting over your hair would you?
Truth be told they are mostly there for back up, but if you are a professional photographer you should already be carrying back up equipment along with you. At least I hope you would!
Throughout my 10 + years of photographing weddings I have never had a need for a second shooter. I'm sure if you have visited my website and clicked on the different weddings I have available for viewing all those photographs every single one, there was not a second shooter....just me.