Not sure if I agree with this.
I found the device (call it what you will) very helpful when driving with strong and gusty cross-winds, which can be pretty "normal" in the Prairies.
Suppose it might help with emergency maneuvers as well, but I have no experience with that.
Agree or not. It is not to prevent sway. Only to help control it once it starts. A trailer should not sway if properly balanced, and hitch adjusted. If it does. You have other problems.
IMO a sway system will help in normal driving when road conditions and wind along with passing vehicles put abnormal forces on longer trailers. I also remember that the recommendation is not to remove in in adverse weather conditions such as rain, but to loosen it so it mainly won't "grab", but still provide some minimum sway mitigation.
It is not needed in normal driving. If yours sways in normal driving. Fix it. Mine is not affected by passing vehicles of any size. With or without the swaybar installed
As for removing. Remember. Any thing less than fully on, is off.