This sort of testing is vital since operational pilots will find a way to depart the jet no matter how departure resistant the aircraft is. It happened during operational testing for the F-22 when one of the pilots managed to get himself into an inverted spiral despite assurances in the Raptor's dash one manual that the jet could be maneuvered with "reckless abandon." If it can happen to a veteran Weapons School instructor pilot, it can and it will, at some point, happen to some brand new B-course graduate--it's just a matter of time.
Incidentally, the Lockheed pilot in the video is Dave "Doc" Nelson, who was formerly a F-22 developmental test pilot, and as he points out, the F-35 really does have excellent high angle of attack (AOA) characteristics. And if what Lea Haubelt, one of the flight test engineers, says in the video is true about the high AOA handling characteristics being better than expected, I'm not sure why the angle of attack limit is set at 50 degrees AOA when they have gone much higher during flight tests.
It may not be a capability that is used often, but extreme AOA performance can be useful at times. A good friend once described pulling more than 63 degrees AOA in the Raptor to escape being from being "shot down" by a high off-boresight missile-equipped Red air threat. It may have been useful for only a few moments, but sometimes it's the difference between life and death.