so a hassy is just the same as any other camera...
Hasselblad made modular, medium format film SLRs. Pros liked them because they were well built and very reliable. They could be customized for used somewhat with different accessories, and they had removable film backs. Before digital we had to carry at least 2 backs: one for BW and one for color. Additional backs if we wanted to switch ISO in the middle of a roll, or see a Polaroid test shot (today it's berated as chimping, but pros have always looked at preview shots, they know it results in better photographs). They also used wonderful Zeiss lenses.
Other than that, yep, a Hassy is just like any other camera: a light tight box with lens, shutter, aperture, and light sensitive materials somewhere inside.
I owned and used a Hasselblad 500c/m for years. It was a great camera, but no better than the other professional quality, medium format cameras I owned and/or used: Pentax, Mamiya, Bronica, Rolleiflex, etc... I used mine exclusively for portraits and at weddings. It was usable hand held, but I preferred the Rollei or P67II for hand held shooting. Once I got a 5D, and it was clear to me that the image quality was similar if not better, I sold the Hassy in a heartbeat. It was a great tool, but it never found a place in my heart like the Rollei.
I have not used the new digital Hassys, but I assume they are similar: high quality, reliable build, customizable accessories and options, Zeiss lenses, and you can add the digital back of your choice with loads of megapixels. But they are still just cameras; the buttons may be different, but the important fundamentals are the same as any digital Rebel or K1000.
As to whether they are practical for professional use, that depends on what the use is. I'm sure they are wonderful for the intricately staged portraits of Annie Leibowitz. Some landscape photogs like them (mostly those who have someone or something carrying their gear). I doubt the late Galen Rowell would have chosen one to do his mountain climbing/landscape photography. I doubt many PJs or sports photogs would choose a Hassy over something smaller and more nimble, but as I said before there are folks using 4x5 Speed Graphics for PJ and sports so there are always exceptions.