[dragonwriter]

> Is there a benefit of using tag URI instead of a regular old URL?

You don't need to control a domain name to issue tags.

Tags issued under an authority (domain name or not) are associated with a time, so remain valid and unique even if you abandon or lose the domain name, etc., providing the authority in the future.

Because tag URIs are explicitly not a scheme that provides location information, the resource does not have to be accessible by a particular protocol for the tag to be meaningful and accurate, and the URI doesn't communicate false expectations to readers familiar with the scheme when the resource is not accessible. (And, for similar reasons, tags don't risk conflicting with actual locators in the future.)