This page is opted out of the index

Nothing here is broken. The page has simply asked to be left out of Google.

When hiding a page is the point

Some pages have no business in search results: internal search, filtered listings, thank-you screens, staging content. The robots noindex tag is the correct instrument for those. It keeps them out of the index while crawlers still follow their links. In that setting the tag is a feature, not a fault.

When the tag outlives its welcome

The same tag turns into a bug the moment it lands on pages written to rank. Staging leftovers are one common source. So is a template that stamps the tag far more widely than anyone intended. Either mistake can pull a whole section of a site out of search. An audit therefore reports each noindex it finds, and a person confirms, one by one, that the hiding was intended.