Access and continuity
A written list of every account, domain and system the business depends on, recording who owns it, who administers it, what it costs and how it is recovered.
One page, and most companies do not have it. Domains and where they are registered; DNS; hosting; mail; the code repositories; the ad accounts and who is billed; the payment gateway; the analytics property; every social profile and the personal account behind it; every SaaS subscription and the card paying for it.
The column that matters most is the one nobody fills in: whose name is it in. A domain registered to a former contractor's personal email is not the company's domain in any sense that survives a disagreement, and the discovery is always made at the worst possible time — during a migration, a dispute, or a renewal that silently failed.
The register is also the fastest due-diligence artefact in existence. A buyer, an investor or an incoming vendor asks for exactly this list, and its absence is itself a finding.
Paying an invoice does not create ownership of a domain, an ad account or an app-store listing. Ownership follows the registrant, the account holder and the developer entity on record. Check each one by name against the company, not against the person who bought it, and correct the ones that are wrong while everybody is still on good terms.
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.