If a vehicle was about to put yourself or your passengers in harm's way, or possibly cause damage to nearby property, you may want a way to avoid such a catastrophe. You might even want a car that could warn you ahead of time to leave the area before the car hurt anyone or anything.
Now, you'll notice that the patent filed by NIO, which back then went by the name NextEV, isn't for only a self-destruct system. That's because, per NIO's filing with the United States Patent Office, the term "self-destruct" is used to describe an electric car's impending, self-catalyzed catastrophic loss. Think of thermal runaway in the battery (like what a limited number of Teslas and other EVs have suffered in recent years), or a massive power fault, rather than a user pressing a big red button that initiates an ominous countdown and, eventually, a dramatic explosion.
NIO has instead dreamt up a system that addresses the more realistic, albeit rare, instance in which an electric car's major systems fail in such a way that the car basically self-destructs on its own. Via onboard sensors and software, NIO hopes its system would automatically detect such a grave outcome and determine a course of action, the ultimate of which involves alerting humans onboard or nearby to flee before locating and autonomously driving itself to a safe space for ending its life. The patent filing includes notes that the doomed car would ideally try and get itself someplace away from structures and preferably near or in water. NIO even thought of what might happen if said destructive meltdown were to occur during charging (the car would spit out its charging plug and speed away, it seems) or when parked in an owner's attached garage (the outcome here is less clear, but we really hope it includes crashing through the closed garage door!) or if a limited-mobility occupant is in need of evacuation assistance (it'll alert nearby pedestrians via external cues to come help).