When setting up OJS for a journal, I was requested to configure OJS to send submission acknowledgement e-mail to all the authors. Set aside reasons for the request, this might be a useful feature to have in OJS.
Of course, I've patched the production system, but not in line with development guidelines. To properly implement it, I'd have to define a journal setting, make it editable somewhere on the journal setup pages, and use it in templates and actions for the last step of the submission process. I'd probably have to define another locale key, to display different message at the last submission step.