In episode 243 of the weekly Hump Day Hangouts by Semantic Mastery, one viewer asked if it is mandatory to create a subdomain when setting up @id.
The exact question was:
For @id, is it mandatory to create a subdomain or will the Amazon object URL be enough? Is there any advantage of setting it up to use a cname subdomain? What link should we use as the canonical URL in our @id? the main money site? the google.business.site? or the maps url?