Common?
Depends on owner or owner/operator.
As we have very small fields compare to there (1/4 of acre, or even less), and you need a lot of manouvering, it is very convinient to have PTO engaged all time, then shut it off on every corner. Especially if you have double stage clutch, and mech engagement.
BTW, I bought just a wide angle joint (about 110$) and put it on an old standard PTO shaft - yellow one. Same PTO shaft we use on manure spreader.
Another one (black joint) came with 2-row corn picker. Last year I sold it, and now I have 2 wide angle of PTO shafts /forums/images/graemlins/smile.gif
Tractor on pic has independent (hand) clutch and mech engagement. I disengaged it shortly just on very sharp turns.