I signed up with BA several years back, I was regularily travelling a route, in business class that amassed points. I was later transferred elswhere and used a different carrier. BA "reorganised" their points system in the meantime.
The net result, through rule changes etc. was a down grading of the value of my points - now effectively worthless. The whole issue was so bloody complicated that I haven't bothered with any scheme since.
Not worth the hassle IMHO