I removed that PTO cover. Only one reason, that I see, for it being there, and that it was years ago used to hold a shield in place over the PTO shaft. Now the PTO shafts are enclosed in a tube that is free from the shaft.
As well, I only use the PTO for two jobs.. rotary cutter and rototiller. Neither would anyone be around the PTO shaft while it is engaged.
Not recommending, but just sayin what I did and handling the hookup of the PTO shaft to the splined tractor stub is much easier.
Also, some PTO shafts have a collar that rotates to free up the balls holding it on. And the differences between those collars and the ones that slide are sometimes very subtle and not so obvious on first blush.