It was difficult to come up with a good topic title. Basically, if you use Blackmagic cameras, do you also use their software for movie production and photo editing? Are you drawn to their DiVinci Resolve software?
Concerning other cameras, I can see how people would buy everything from the same company. There are lenses, for example, that you can only use for specific models. I'd opt for products that can be compatible with other brands, though.