A 200 response is the server telling the browser everything worked: the request was received, understood, and the page loaded without issue. It's the baseline every other status code gets defined against, the outcome you want on every page a visitor or crawler actually requests.
For SEO, 200 is the status a page needs to carry to be crawled and indexed normally. A page returning anything else where a 200 is expected, a soft 404 that renders content but reports an error code, or a 200 on a page that's actually broken and shows an empty or error state, confuses both crawlers and monitoring tools. Server logs and crawl reports are worth checking periodically for exactly this kind of mismatch: pages that look fine in a browser but aren't actually returning what they should, or pages quietly serving errors that nobody noticed because the visible content still rendered.
