OK, I think I get it.
So for example, lets say my crowd of 50 people starts 10 feet away from me, and ends at 15 feet, for arguments sake. What I think you're saying is I can do one of two things:
1) Put flash into Auto mode, set it to f8 (f8 covers the range 10-15 feet according to the dial). It doesn't then matter what settings I have on my camera lens (unless it was really really bright) - I can set it as f5.6 or f8 or f11. The flash will then throw as much light as is needed. Or
2) Set it Manual mode for full flash power and then set the camera lens according to the ranges on the flash dial. Using the example above, again, f8 if the crow is 10-15 feet away.
Is that right?