My tractor automatically engages FWA. I have found that when I am maneuvering in a tight spot it sometimes has a hard time figuring out when it is needed (the sensing is some kind of torque sensitive device, likely a torsion bar) and it can be out foxed. In those situations it can be hard to turn and really digs the ground up more, but that is rare, and I am learning when that occurs and shut it of, or accelerate after I have turned. If you have ever driven a conventional 4wd truck and tried to turn and accelerate you will know what I mean. And yes, it is harder to turn (more than a little bit) with it engaged. Especially with higher traction tires (like R1's).
With the auto engage, I think it is working as it should in a turn -- it senses a differential pressure between front and rear wheels and applies power to the front axle, which may not always be better.
Like most things, if you wind up the engine and drop the clutch, you will eventually break something.