Security
The chain of accounts that can reset each other's passwords — and therefore the real security level of every account in it, which is the level of the weakest.
Write the chain down once and it becomes obvious. The advertising account is recovered by the business account; the business account by the mail account; the mail account by a phone number and a backup address; the domain is recovered by the registrar account, which is recovered by mail. Anyone holding the mail account or the registrar holds everything downstream of it, whatever is configured further along.
Two accounts deserve treatment above the rest, and they are the two that are usually forgotten: the domain registrar and whichever mailbox is the recovery address. Compromise of the registrar allows mail to be redirected, which allows every other account to be reset in sequence.
For social profiles the equivalent question is who holds the roles. A business page owned by one person's personal profile disappears with that person — through a dispute, a hack, or simply their leaving. Ownership belongs to a business account with at least two administrators on separate credentials.
A founder's personal address is on breach lists, has weaker protection, and leaves with them. Recovery for business-critical accounts should point at a mailbox on the company domain that exists for that purpose, is protected with hardware keys, and is not used for anything else.
The definitions are the easy part. Whether the figure on your dashboard was computed this way is a different question, and usually the more expensive one.