Why do some people take two or even three SLRs with them when traveling?

Each lens performs differently when encountering different scenes. Bringing two SLRs can quickly switch to the scenery and pictures you want. There is no need to change lenses midway. Focus on the subject or target scenery with telephoto. The wide angle is responsible for big scenes, and the styles of pictures taken are different. If there are many lenses, it is normal to bring two or even three SLRs. When I go out, I usually bring two SLRs, one with telephoto and one with wide angle.