sometimes, you just need an extra set of eyes. Sometimes you can look in your rear view mirror and see someone stopped at the crest of a ledge trying to look over the hood or out the door when they have "lost" the line.
Sometimes I can use the CB to tell the guy behind me that they are lined up perfectly and are good to go or tell them something like, "steer driver a little bit and come on down." I don't have to get out of the truck which helps keep the trail moving. You all know that as soon as the leader opens the door to get out, EVERYONE stops to open their door and get out!