A good photographer can get the majority of what you need on their own. You'll want a second photographer if the venue is rather large, and there is a lot of ground to cover. Or, if your main photographer is taking pictures of the wedding party, do you want someone to cover cocktail hour? Then yes, you'll want a second photographer. I do love to have a second photographer with me for assistance, and you get more of a variety of images. But is a second photographer necessary? No.