Besides rejecting invalid commands, what is another common real-world use of a MessageDispatchInterceptor?

A very common use is attaching a correlation ID to every command as it's dispatched, so that a single originating request can be traced consistently across every service, command, and event it touches through the system — the same tracing idea commonly applied to incoming HTTP requests, adapted here to commands. Since a dispatch interceptor runs centrally, once, on every command regardless of type, it's a natural single place to attach this kind of cross-cutting metadata without needing every individual command handler to remember to do it. Centralized audit logging of every command flowing through the system is another common use, for the same reason: registering the logic once in an interceptor guarantees it runs consistently for every command, rather than depending on each command handler remembering to log itself.