In macOS Mail and iOS Mail, when you reply to an email or send a new one, you can choose the "From" address: The options are the usual accounts you have set up, plus, now, a "Hide my Email" proxy generated on-the-fly. I've found it very handy on several occasions.
* accidental semi-spam (people sending emails to someone at one of the domains I own, mistakenly) where I wish to notify them that they got the wrong email, but don't want to divulge my main email (and name).
* support emails from services that I signed up with using "Hide my email". When replying, the "From" defaults to my main email, but again, I can switch to "Hide my email".