I might add, I've been a die hard roady for 45+ years. Never in my life would I have thought that I might use any bar other than a regular drop bar. Unfortunately pain is a motivator to try something new, otherwise I would still be using regular drop bars. From my perspective, I have found that flared bars give a wider, more stable position in the drops, which comes in handy on rough terrain and when descending. On my 29er hardtail, with flared drop bars, I have been able to coast at full speed down 8+% grade, very rough/washboarded forest roads. (Over time I rode these descents on flat bars, regular drop bars, full rigid bikes, full suspension bike, with flat bars.) My fastest descent times are on my 29er hardtail with flared dropper bars. My FS ride with flat bars is the next fastest.
In the past, my buddies used to be significantly faster than me on these descents. Last year, they were asking how I had become so much faster.
I believe that is is the stability of the flared bars and being able to tuck on the drops in a more wider more comfortable aero position than either flat bars or regular drop bars.