Why it matters to a buyer
Google's own guidance calls faceted navigation the most common cause of overcrawling problems it hears from site owners, because every filter combination generates a new URL and a large catalogue can produce millions of them from a handful of products. For a buyer, unmanaged facets waste crawl budget on near-duplicate pages instead of the pages that matter, and can bury genuinely valuable pages, like real category and product pages, under noise that never should have been crawlable in the first place.
How it is measured or applied
The fix depends on whether a given filter combination deserves to be indexed: high-value combinations, like a popular colour within a category, can be given clean, crawlable URLs with their own canonical and internal links, while low-value combinations are kept out of the crawl entirely, through robots.txt rules, URL fragments instead of query parameters, or nofollow on the filter links themselves. It is monitored by watching crawl stats in Search Console for a spike in URLs crawled relative to real pages, and by reviewing server logs for how much crawl activity is going to filtered URLs that were never meant to rank.
Sources
- Managing crawling of faceted navigation URLs, Google Search Central
