sameAs
Also known as: entity reconciliation, identity links
A structured data property listing other URLs that describe the same entity, used to connect a page to an identity that already exists elsewhere.
An Organization node with a name is a claim. The same node with a sameAs array pointing at a Wikipedia entry, a Crunchbase profile, a LinkedIn company page and a verified social account is a claim a machine can check against records it already holds.
That is the whole function: reconciliation. It turns a string into a thing.
sameAs is worth less when it points only at profiles you control and nobody else references. Three social accounts with no followers do not reconcile anything. One authoritative third-party reference does more work than five self-published ones.