In my opinion, if you're a wedding photographer, this lens is a must-have. I use it for around 25% of my images at any given wedding, but they are important ones. The focal length and the fact that it is F2.8 through out the entire lens is what makes this lens so special, it allows you to capture shots at the ceremony without you having to get right in the bride and grooms faces. I can easily work the sides and back of the venue and zoom in to capture these important images.
With a 200mm focal length, I also believe this lens allows me to capture very genuine moments, because people tend to show more emotion and act as themselves more when they don't have a camera pointed in their face.
The only time I really don't use this lens is for getting ready shots. I feel for these images I want to use a wider angled lens so that I can capture much of what is going on around and in the room....Which leads me to another great lens below.
This is my work horse. It's reliable and very versatile. I use this lens for about 60% of my images. This lens will be on my camera at some point during every part of the wedding (getting ready, first looks, portraits, family/group shots, ceremony, reception, etc) The focal length of 24-70 is very useful.
The focal length of 24-70 has also helped me capture some of what I call my "Signature Images" these images usually are shot at a wider angle and will show off the subjects incorporated with a large sweeping landscape.
Even though this lens and my 70-200mm are f2.8 and can shoot pretty well in dark situations, it is still advised that you have atleast one the following in your bag....Prime Lens (see below)
This is the newest weapon in my arsenal. You will notice right away, that unlike my other two lenses, this one can go as low as f1.4. This may not seem like a big deal, but the difference between 1.4 and 2.8 is greater then one would think (at 1.4 your camera's sensor can collect 4x more light then at F 2.8) To make this very simple......This lens can see in the dark (OK not literally), but during those very dark situations you encounter when shooting weddings, such as reception lighting, portrait sessions at night with very little ambient light, etc, this lens will get you very high quality usable images.
On top of all of this, the lens is extremely sharp and produces very nice bokeh, only down side is with it being a prime lens, you won't be able to zoom in and out (well you can, but it requires you moving your feet!)