Hitec HV Digital servos can be programmed to to only allow so much torque be applied. This protects them from being over-torqued. I use this feature from time to time when I have only one servo on a large control surface.

I have had several servo failures. I have had a brand new plane's aile servo lock in the up position at about 15 degrees (33% Extra). After rolling straight up, I got it figured out enough to land the plane w/o further incident. There were two servos on that surface. I know the good one could not overcome the one that was locked up, thus the rolling assent.

On my helis, ... I have had several servos lock into position. Inspection typically revealed that broken gear teeth were jammed in the gears preventing them from turning. I have had one that electrically would not allow it to move. Took the power off and it would move. Recently I have had a couple failures that just buzzed as they were trying to position themselves and shut off, but could not physically move. They were both free for movement. Gears were stripped right out. I suspect that most of the heli servos that failed for me were due to crashes.

I had the flap servo burn out on the Sprint. I suspect that there was more load on it than expected.