I've already mentioned many reasons why this lighting is superior to additive lighting (using a flash outside), but here's another very important one:
Subtractive lighting by its nature keeps the subjects married comfortably to their environment keeping the look genuine--and, well, natural!
Additive lighting, with flash outdoors, very obviously divorces your subjects from their environment--it pulls them out or appears to bring them forward to the camera--as though the natural background light repels the artificial light of the flash.
That's just how it looks and feels to me. Take a look at my portraits again here and compare them to other photographers using flash outside. Do what you think works best for your clients.
The tools I use to block unwanted light are called Gobos or Flags. (Both terms we use in the world of cinematography; not used much in the still photography world today.)
A Flag is generally a black flat and refers to something you could hold by hand or mount to a stand.
Gobos (from: go-between) as I use them are much larger things that are already on my location; either man-made, like a building, house, porch--or something natural like a tree, a forest or hedges.
So, revisiting my images from the previous 2 blogs plus a new one, I've added some data and short descriptions about the subtractive light used. Enjoy and feel free to ask any questions on this topic.
By: Jerry W. Venz, Excerpted from my forth coming book: The Best Light Money Can't Buy!