It would be useful to be able to prevent Moodle sending emails from users own email addresses and instead to send everything from the server's configured noreply address.

One scenario where this would make sense is in a large institution which has a centralised mail relay hub which controls the outward email from all of the institution's web applications. Normally a service like this will not be configured to relay emails with arbitrary "from" addresses as this is often seen as a security risk.

In addition, it could be argued that sending an email which appears to come from another email service is "spoofing" and that institutions should not do this without express permission of the user. (For the record, I don't necessarily agree with this statement but I know people who would argue along these lines!)