No, it is not. Signals have a relatively limited usefulness within Django.
See the thread at Is this a good use case for the `post_save` signal? for a more detailed discussion about the usage and value of signals. I would also suggest you read Django Anti-Patterns: Signals | Lincoln Loop for a well-written opinion on this topic - an opinion with which I agree.
This would be the only situation in which I would use them, and then, only if that other app was written by a third-party.