My limited understanding is that not all WB functionality is the same in all camcorders. Some cameras are more capable than others in adjusting the color temp, some not so much.
For example, my sony HC7 is limited to a certain maximum color temp change. The actual "depth" depends on the sunlight, water clarity, etc..
I still think this MWB option of this rig has value. This MWB option in this S10 rig may still have some merit in some situations.
FYI, I manually set my WB often even when shooting macro / upclose subjects with artificial lighting. I've found that even a foot or two distance of the light from the video heads to the subject effects the color temp.