There are a lot of benefits to having a second photographer at your wedding, you will undoubtedly receive a more diverse array of photos, your main photographer can spend more time shooting the important moments while the second shooter can organise equipment and round up people for photos; and you are more likely to capture all the important moments in your wedding.
Every photographer has their own style of shooting and editing. Some shoot a lot of wide angle photos so the viewer of the image can get a good grasp of the feel of the location which the photo was taken at. Other photographers prefer to tightly crop around their subjects, to focus on the bride and grooms facial expressions and body language to set the mood of an image.
One style is not necessarily better than another, so it is nice to have a mix of different photographic styles in your final wedding images.
2) More hands to distribute workload
More photographers generally means more photographs are taken on your wedding day, but it also means there is less set-up time required for location photos, and it is quicker to organise family members for group photos.
The less time it takes a photographer to organise people at the wedding and set up their equipment, the more time they have to take photos and carefully consider the composition of their shots. Your wedding day can a very busy and stressful for both you and your vendors, so having an extra pair of hands for organisation can make a huge difference!
3) Miss less moments
During your 12+ hour wedding, it is inevitable that your photographer will miss at least one moment that would have made an amazing photograph. It is not uncommon for photographers to take over 2500 images in just 1 wedding day, but sometimes it is logistically impossible to be in the right place at the right time.
A good example of this is during the bride and groom's preparation at the start of the day. If the bride and groom are getting ready in separate locations, its paramount that you two photographers, one with the bride and one with the groom, so no important moments are missed!
Similarly during the ceremony, it is highly recommended to have two photographers, one that is taking photos of the bride and groom, and another taking photos of the audience members as they watch you tie the knot. Some of the most precious photos that are captured on day are the reactions of friends and family during the ceremony!