If it were the sixties -- the last time I really worked with lights -- I'd agree with you cjogo, but with Nikon's i-TTL you'd be nuts to screw around with guide numbers and go manual on the flash. Maybe you have to do that with Canon, but not with Nikon. Yes, the camera goes manual and you control shutter speed and aperture separately instead of being in aperture priority and letting the shutter speed drift, though if you're just bouncing flash off a ceiling or wall, in many cases you can do a pretty good job in aperture priority.
But when you're trying to balance ambient and flash you can't do that. You crank up the shutter speed (in the case of #1, shutter speed was 1/1250 in order, as Joe McNally puts it, to make the available light unavailable.) Aperture was f/2.5 for a shallow depth of field. Once those two were under control, it was a matter of controlling flash intensities. With an SU-800 I can hold the camera in my hand and control flash intensities on three groups of flashes. And with digital I can look at the back of the camera and get a pretty good idea of what's happening. You can't beat i-TTL and a flash setup you can control from camera position. Nowadays going to manual flash is sort of like using a view camera with a lens cap as its shutter. There was a time when that made sense because that's all that was available, but not any more.