Quote Originally Posted by AndrewH
When using the RF back you get all of the LF flexibility. You give up some quality in the lenses, though, depending on what MF lenses you are using. Someone here can correct me, but I am pretty sure that (for the most part) with each step up in format you lose some resolving power in the lens. While using the larger film area more than makes up for this when enlargements come into play, when you use a RF back, you are still in 120 size film. This isn't to say you cannot make magnificent prints from a RF back, that isn't the case. Just being technical :-)
It all depends on the lens, Andrew. On 120 roll film, in 6x6 cm format, my 55mm Rodenstock Apo Grandagon (which covers 4x5) outperforms my dedicated 50mm Hassleblad Zeiss Distagon. My 110mm Schneider Super Symmar XL (covers 5x7) outperforms my dedicated 120 mm Hassleblad Zeiss Makro Planar. In addition, the superior performance of these two example LF lenses easily extends to the 6x12cm roll film format as well.

The main reason for using the Hassleblad (or my Hasslebladskys) is that they are much faster to set up and shoot (not really of a virtue to me - except for doing film testing).