The typing version is still useful when you want to communicate that the result conforms to a certain interface, which doesn't include mutability in the case of

The typing version is still useful when you want to communicate that the result conforms to a certain interface, which doesn't include mutability in the case of Set, but not the exact type. Edit: I see that he imported the typing Set, which is deprecated, instead of collections.abc.Set, which is still useful, so your comment is correct.