Second Shooter?

Jacob and I have made our wedding photographer decision... but I'm not going to say anything here until the paper work is signed and the date booked!

I do have a question for you though... how important is a second shooter?

We're planning on about 100 guests. For those of you who only had one photographer, do you wish you would have had two? And vice versa... those who had two, do you think one would have been sufficient?