Agreed, leaners can be dangerous if you try to drop 'em against the lean. I don't have the experience nor the equipment needed to attempt this.
Learned my lesson on leaners some years ago. Got a face cut in a big red maple, it had some lean. Started the back cut, got a couple inches in and hit mush. Darn carpenter ants. Heard some crackling sounds. That was all I needed... took off running to my escape route.
Like Lot's wife I turned to see the tree chair. It broke off around 15' up, rolled and hit the ground a good 10 feet from the stump. My knees got shaky, sat down on the ground for a few minutes to rest.
Never again. I won't cut large leaners without a length of chain around 'em anymore.