Uptime monitoring checks a site's availability on a fixed interval, independent of real visitor traffic, so an outage is detected within minutes rather than whenever a visitor or team member happens to notice. Beyond the direct visitor-facing cost, unmonitored downtime has a crawl-side consequence too — search and AI crawlers that repeatedly fail to fetch a site reduce how often they come back to check it, an effect that persists after the site is back up.
See Website Downtime and SEO for the full picture.