This might not happen often, but here’s a great example of a video that requires B-roll to be the most useful part of a project. Take a silly thing like football (I like football!) and an even sillier thing like dog shows (I like dogs!) and put them together.
The premise is “What breed would play what position on the football field?” The video is showing the dogs, essentially putting names to faces, while the two guys strategize on building a dog team.
Here’s the roster breakdown, with the caveat “For the sake of argument, these dogs have opposable thumbs and can understand the purpose of sporting contests.”
UPDATED to fix the video, which was inexplicably embedding something else into the post for some browsers.