Having far more fine control over, of all things, email. Being able to operate an entire domain and control what happens with every email address in it. I now have a different email address for every legal entity I interact with, sometimes on a per-interaction basis. If I get spam, I know exactly where they scraped the email address from and I can set that specific email address (plus or minus any other data such as which domain it's coming from) to reject with a custom response or display any other behavior in the email protocol, which is surprisingly extensive once you start looking at it.
Having far more fine control over, of all things, email. Being able to operate an entire domain and control what happens with every email address in it. I now have a different email address for every legal entity I interact with, sometimes on a per-interaction basis. If I get spam, I know exactly where they scraped the email address from and I can set that specific email address (plus or minus any other data such as which domain it's coming from) to reject with a custom response or display any other behavior in the email protocol, which is surprisingly extensive once you start looking at it.