In this photographer's case, the answer is VERY.
This past weekend I directed a music video for Chrissy Murderbot. The nature of the shoot involved the playing of a footwork video game. We filmed dancers on a greenscreen to composite into the video game footage. Lighting a greenscreen can be very difficult, especially when one is filming someone's entire body. Inevitably, shadows will be cast, and that makes the process of removing the green screen that much harder.
One solution to this problem: huge lights. Unfortunately, I don't have those.
Working with what we had, we wanted to light the backdrop and floor as evenly as possible while maintaining an interesting look on the dancers. We got the setup arranged as close to what we wanted as we could, but we lacked an adequate fill on the shadows cast by the wrinkles of green screen cloth on the floor.
One last challenge was that we were filming two dancers at the same time. We had to keep the framing wide and light both subjects evenly.
Here's what you don't do:
Step one: Take one large softbox. Insert into said softbox two comically-large CFL bulbs which each have 250 watts output equivalent output. A-clamp said CFL bulbs to the internal framework of aforementioned softbox. This is (read:should never be) your fill light.
Try not to move it around too abruptly, as should the precariously mounted lights come unattached, they would most definitely break.
Step two: Clamp the light assembly (hereafter referred to as Illegitimate Softbox Rig Assembly) to a very long bubble level you found laying around on set when you arrived. Hopefully you've just selected a recently renovated space as to accommodate this need. Do so using any type or variety of clamps you have (in this case, a super clamp and two A-clamps). Place this on top of two tall light stands and clamp them as to prevent the delicate Illegitimate Softbox Rig Assembly from facing directly towards the ground. Proceed to extend both light stands simultaneously until reaching maximum
Your Illegitimate Softbox Rig Assembly is also useful for other things, such as replicating the light from a TV. For added believability, wave some sort of light-blocking device (i.e. cloth, jacked, one's own body) in front of the diffusion for a "realistic" screen-flickering effect.