Use case:

You have a non-template bibliographic citation, and you want to re-use some information (but not the rest) in a citation template. This means open ref #1, copy something, close ref #1, create ref #2, paste in one bit, close ref #2, re-open ref #1, copy something else, etc.

It would be easier to do this if you could skip all the re-open and re-close steps, and just have both dialogs open side-by-side.