"Authorized addresses" not documented

[notDavid]

https://app.simplelogin.io/dashboard/mailbox/xxxxx/

Authorized addresses
Emails sent from these addresses to a reverse-alias are considered as being sent from x@x.x

Here are the Docs.

I understand what the feature does. But it's not documented, for example does this result in also applying the "Default Display Name" of another Domain ?

So what exactly does adding a mailbox here result in (perhaps, more than just "authorizing" it) ?