Weddings are a special time for a bride and groom. In most cases, they have selected a professional photographer to capture every special moment. If you are a guest at a wedding, be mindful that your attempt to get "your" picture of a special moment, could possibly hinder the professional photographer from doing their job. If you are the bride and groom, inform your guests that you have hired a professional photographer and you would prefer if no pictures were taken during any ceremonial portions of the wedding.
Common courtesies can prevent the bride and grooms first dance, from looking like a line dance.