PaulMD, a big advantage is that you do not need to invest in 2 systems, learn the advantages and disadvantages of each, different handling charactoristics, and learn just one set of lenses plus reduce a potentially large investment in accessories such as filters. Just cost out a totl new 35mm body wide angle, normal, portrait, moderate tele and telephoto lens plus 3 macro tubes, doubler, circular polarizer, an assotment of about a dozen filters, case, and other accessories. Use something like a Pentax LX and price out the wlf, metered prism and nonmetered prism and ad the motor drive and you'll see the savings in having only 1 system. For the price of that system you can add the shift lens to the Bronica or the zooms and have change left over, especially at today's prices.
The multiple viewfinders, wide range of flash sync, removable backs and several film formats that include 120, 220, 35mm, 35mm panaramic and Poloroid pack film makes for a fairly universal camera.
No, there is a limit on the low end of the lenses but there is the 27mm that has the coverage of a 17mm with 35mm and on the upper end there is the 1000mm and you can add the 2x extender to get to 2000mm so not too shabby there. Plus there are a couple of macro lenses, a shift lens and a few zooms.
I have no particular rhyme or reason as to when I pop on the 35mm back vs a 120 but, when only doing snap shooting of get togethers, I generally will pop on the metered finder, the 40mm lens, the 35N back, pop in the screen with the 35mm film format lines and, speedgrip. Holds and handles like a 35mm slr. Use it in AE mode. It has 40mm coverage on 35mm which is what I also shoot if I took the Leica. If I want wider, I'll slap on the 120 back and have the coverage of a 27mm on 35mm. So, carrying the backs that are lighter than lenses gives me different coverages, i.e. I'd have to carry 2 lenses to do the same thing with a single format system. Also, this way, I do not have to then start digging out the filters for the lens change.
Now, admittedly, I do violate the single system advantage as I do have a Leica CL system with a 40mm and 90mm lens. And recently save an old Asahi S2a complete with 4 lenses from a thrift, have a Rolleiflex, Vitto II and Zeiss Ikonta 35mm, a 1.2 frame Konica, a pair of Yashica FX-3s, a Polaroid 180 and 195 along with a couple of SX-70s and about 20 of the auto pack cameras plus a few others kicking around. Only regular users though are the Bronica and Leica. The Rollei needs the shutter serviced which I'll do and the rest are closet queens. I do plan to try out the Asahi just to see the condition of the shutter.