201 201 Created

The request succeeded and a new resource was created (typically after POST requests).

When you'll see it

After a POST or PUT that created something: a new order, user or file. It's mostly seen in APIs and rarely on normal web pages.

That the Location header points to the new resource, so the client can fetch it.
That the code is only sent once the resource really exists, not when it's merely queued. Use 202 Accepted for queued work.
That a retried request doesn't create a duplicate. An idempotency key prevents that.

HTTP/1.1 201 Created
Location: /api/orders/1042
Content-Type: application/json

{"id": 1042, "status": "new"}

Not relevant for SEO crawling. Typically returned by APIs, not web pages.