They are talking about MTA output. Mail input and archiving are still important factors. I personally want to control my input addresses. Hosting your own you

They are talking about MTA output. Mail input and archiving are still important factors. I personally want to control my input addresses. Hosting your own you can get funky wildcard postboxen. Hosting your own you can archive all the mail without 3rd party approval. I can see the advantage of the small amount of outbound being via someone else.