The main use for a V-flat in my opinion would be 1. To add fill light to your subject 2. To subtract light from your subject 3. To bounce light onto a backdrop spread evenly 4. As a flag to block light or glare (an unwanted window) and 5. As an actual backdrop.
Until now V-flats for the most part have been a DIY item. Why has it taken so long for someone to come up with this simple yet brilliant idea of making them foldable and avoid those $350 shipping charges.
Why are V-flats so loved by pro photographers in the studio? Lets say for example you are shooting a dress, having a big piece of white or black surface that is easy to throw around can allow you to fully light a model from head to toe without worrying about under exposing the lower part of it. Butterflies and big soft boxes are great as well but a V-Flat is just so practical.