Thanks for the comment sorry for the late response... many of our customers are using IronWorker for:
1) Scheduled Emails: IronWorker allows an easy way to schedule emails to go out at different times. Think cron in the cloud.
2) Asynchronous Calls: If you're sending a lot of emails, you can pass the processing off your web server into a worker very easily. Almost like a thread in your code, but to another platform freeing your resources.
3) Batching: If speed is of the essence, you can parallelize the process with workers.
4) Other: There are lots of other things you can do like send emails with a delay, insert merge fields, process content or templates before sending, etc.
All that said it's important to find what's right for your use case. Our customers help us learn what our value is and then we try and communicate that to others.
Hopefully that helps a little.
Thanks again, Chad