One example of where it's used: to enforce correct usage of mutexes. Rust's `Mutex<T>` owns the data it protects. When you lock the Mutex, you get a reference to the data inside it, but it's impossible (a compile-time error) to store a copy of the reference beyond the point where you release the lock.
Cool. So the fifth point is largely nullified, which is a big one -- that the features of Rust would at least be useful in typical safety-critical code.
