It's very friendly to large providers. The amount of computation needed to send to a domain is the same regardless of how many emails you send so large provider

It's very friendly to large providers. The amount of computation needed to send to a domain is the same regardless of how many emails you send so large providers can amortize it over more emails. And large providers generally operate their own infrastructure, which implies they already have a lot of idle computing capacity during off peak hours, and "off peak" is staggered across regions. But even if some large providers refuse to hash outgoing mail, they can still verify incoming mail. The interesting benefit is that a small email provider can burn some dollars in computation once to avoid having their mail discarded by a large provider's spam filter indefinitely.