Examples of why to use @bodyRoot vs @body

[artsiommiksiuk]

https://typespec.io/docs/libraries/http/operations/#body-vs-bodyroot

I can't find a good reason to use @bodyRoot decorator anywhere, and also finding it confusing whenever I see it, either in language or emitter. Idea is clear but also seems pointless.

Documentation mentions that @bodyRoot might be used for some templates cases, which I also can't figure exactly.
So, could somebody give an example of why @bodyRoot exists?