What kinds of consumers, you mean? I've found them most useful for integration with new hosted services that haven't yet made it onto the external services list

What kinds of consumers, you mean? I've found them most useful for integration with new hosted services that haven't yet made it onto the external services list provided out-of-the-box by Github. For instance, when you want to try out (or develop) some new project tracker or hosted CI solution. I'm a little surprised they still don't offer any auth configuration for webhooks the way they do for most external services, so you're stuck with basic auth on the post-receive URL.