Looks to me like some people are talking past each other here. Maybe not and everybody but me knows when a clutch type posi is meant and when a locker is meant.
My own experience is that a clutch type posi is highly desirable for general use and a locker is highly desirable for specific needs. I had an early Bronco ( Spring production with a newly available 289) with a clutch type posi front and rear and never had a problem - despite warning of a slip steer effect in front I didn't see it. Drove that Bronco from Florida beaches to North Idaho with no traction control issues. I did see times on a soft surface throwing roostertails from all four corners and sliding sideways but all the wheels were driving. Compare that with the long ago very early full time 4X4 GMC with an open differential at each axle and open differential in the middle - jack one wheel up and those things wouldn't drive off the jack. If I haven't made myself clear under no circumstances would I prefer an open differential including glare ice and black ice - assuming good tires and all the rest of it. I did have an F250 highboy 4X4 that would bring the back around at the slightest provocation but that's another story of weight distribution and wheels and especially hard cross bar type tires.
Again a modern traction control system is all around better than any of the old systems but who wants to take a fancy new Audi or Benz up a logging road in deep snow - and it's imperative to have clearance for good chains but that's another issue.
