I am absolutely not a 1-1 type of person but sometimes it happens to me that I cannot produce what I want and, exactly because I have many cameras, lenses, lights and so on, I get into a gear changing routine which add chaos to confusion. Usually, when I get back to my mind and use what I always used for a certain type of picture I get much better results. I guess that something similar might happens to other people too, and that might be a reason for the birth of the 1-1 myth. Also, when traveling sometimes a lot of gear really gets into your way to taking pictures, especially these days that photographers are often regarded as terrorists wanna-bes. Finally, even if it is not good for picture taking I can only agree that 1-1 is good for your back... 🙂
GLF