Although this way sounds weird, but Amazon feels if a drone should fall, then it should not fall as a whole heavy drone and just fall as pieces of components.
In the patent, it is explained how fragmentation controllers will be active in case of system failure in drones, such as exploding batteries or problems with the propeller. The computer will quickly learn the flight path of drones, weather conditions and the environment before making the drone unravel itself. You can see an illustration of this patent in the picture below.
"In the process of self-disassembly, one or more parts or components of the unmanned aircraft may be released," the Amazon patent wrote. "By doing so, the weight, speed and coefficient of air attraction and other factors related to unmanned aircraft can be changed."
Of course, even though it has earned this patent Amazon could have just done the experiment and will not realize the concept on this patent.