As a CA you can issue certificates for other domains as well which might be undesirable. There are existing mechanisms such as Name constrained CAs and proxy ce

As a CA you can issue certificates for other domains as well which might be undesirable. There are existing mechanisms such as Name constrained CAs and proxy certificates to reduce this scope. While they were originally considered there are issues with them. There is no widespread support for either and there is no way to know whether both sides support them. DCs allow for a extremely minimal subset of what you might need to issue credentials with your own lifetime and it only affects you. DCs are cryptographically bound to the leaf certificate as well. A bunch of this is documented in the draft.