The benefit it has is that the 'shop.' subdomain can't be guessed from the DNS records. I get a lot of spam to <randomname>@mydomain.com. Of course, if someone

The benefit it has is that the 'shop.' subdomain can't be guessed from the DNS records. I get a lot of spam to <randomname>@mydomain.com. Of course, if someone sees my email address, they could certainly infer a new one. But I'll deal with that if and when I get singled out. I don't think the spammers often actually look at the millions of addresses they use. If I start getting spam on a particular alias, I can set up filtering rules to delete them.