It's worth pointing out that another use case for this feature is sharing. If my wife and I are collaborating on a project, I'd like to be able to give her (or my mom or sister, none of which are normal EN users) an email address which she can use to contribute notes to our shared notebook.
When I'm asking others to help me collect information for a project—whether it's taxes, recipes, or family documents—asking them to add a specific token to a subject line is one more point of complexity to include in the request.