Consider a security interface of some sort, e.g. such that validates a security token.
With a normal interface, it is easy to implement it and ignore the token (allow all), siphon off the token, add a backdoor, etc. If a class doing that is somehow injected where a security check is done, it can compromise security.
Now with a sealed interface, there cannot be new, unanointed implementations. If you get an object that claims to implement that interface, it's guaranteed to be one if the a real, vetted implementation that does the actual security check, not anything else. You've just got rid from a whole class of security bugs and exploits.
Consider a security interface of some sort, e.g. such that validates a security token.
With a normal interface, it is easy to implement it and ignore the token (allow all), siphon off the token, add a backdoor, etc. If a class doing that is somehow injected where a security check is done, it can compromise security.
Now with a sealed interface, there cannot be new, unanointed implementations. If you get an object that claims to implement that interface, it's guaranteed to be one if the a real, vetted implementation that does the actual security check, not anything else. You've just got rid from a whole class of security bugs and exploits.