Also helps turn with a wide front end like yours has in a variety of conditions, like on hills, or when on wet grass, or with a heavy load on the rear.Using one brake to help turn works best with 'narrow front' tractors whose front wheels can usually turn much more sharply.
Adjust both sides to evenness if you latch (who doesn't as default?) the brakes.
Most everyone, so far as I know. I've been driving tractors for about 65 years and have never heard of anyone leaving the brakes locked until I read a few people say that here. I use the brakes individually all the time, and only lock them when I want both to be engaged when the parking brake is set, or maybe when I take it on the road.
Terry