Why use transform_view?

7-1. Our implementation of zip_iterator uses transform to generate its nested
     ::type.  Would using transform_view instead yield any advantages in this
     case?

transform_view might yield some benefit if the caller doesn't examine all the elements in the "zipped" element, but this is a strange case — it's unlikely someone would zip the contents of multiple sequences and only look at a subset of those sequences when iterating.