Okay, but using high speed sync (or Nikon's Auto FP sync) at faster sync speeds than the one supported natively by the mechanical focal plane shutter you lose one stop of light for every stop that you go above the sync speed, i.e., with the Fuji's 1/125s sync speed, a 400Ws unit effectively becomes a 200Ws at 1/250s, 100Ws at 1/500s, and so on. With a central shutter such as the ones in Hasselblad's X series lenses there should be little loss of flash output if the flash duration is short enough compared to the exposure time (with Quadra Action heads the 400Ws pulse has a 1/2800s t.5 duration; 1/5700s for 132Ws) or Nikon's speedlights (SB-5000 M1/1 1/980s, 1/5160s at M1/8 and so on), I would imagine 1/1000s should still work nicely. So with the Hasselblad's CS lenses you should be able to accomplish similar things in terms of balancing flash with daylight using a smaller flash unit that has 1/10 of the output than what you would need with the Fuji's focal plane shutter. Of course, if you need a lot of depth of field then this consideration may not be primary, but for individuals and couples, there is not so much depth of field needed, and so a small flash can be sufficient.
Thus the use of a central shutter translates into lighter lighting gear, which is important when working outdoors on a hot July day. Carrying heavy flash gear, stand, modifier, and the necessary sand bag around when shooting the formals in the summer heat can mean I will be sweaty the whole day afterwards and my cameras will feel sticky the rest of their lives. With the Hasselblad, a much lighter flash could do the job; problem solved; no sticky cameras and a less sweaty photographer.
High speed sync solves the other problem which is how to get access to wide apertures when shooting with flash and bright ambient light, but it's not the problem which I have.
Quite a lot of wedding photographers seem to solve the portability issue by simply using straight head on flash on a stand without modifiers, to avoid the effects of wind and to get enough light to balance with sunlight, but I reject the hard light of direct flash even as fill, it doesn't provide proper gradations on faces and 3D features of the subjects.
