Faceted Navigation
Faceted navigation lets visitors filter listings by attributes such as size, colour, price or brand. It is excellent for users and hazardous for SEO, because each filter combination can generate its own distinct crawlable URL, multiplying the number of indexable pages exponentially.
Why it matters for your rankings
Faceted navigation is the most common cause of catastrophic crawl budget waste on ecommerce sites. Five filters with six options each produce tens of thousands of URL combinations, nearly all of them thin, near-duplicate and worthless in search.
Google then spends its crawl allowance on colour-and-size permutations while new products wait weeks for indexing. The pages that do get indexed compete with your real category pages, splitting relevance across variants nobody searches for. The nuance is that a minority of facet combinations have genuine search demand, such as 'black running shoes'. Those deserve indexable, optimised landing pages. The rest should be crawlable for users but invisible to search engines.
How to check it on your site
Measure the damage
Compare the URL count from a full crawl against your sitemap count. A large gap usually points at facets.
Identify valuable combinations
Use keyword research to find which filter combinations have real search volume. Those become indexable pages.
Block the rest
Use robots.txt disallow rules for parameter patterns, plus canonical tags pointing at the clean category URL.
Check crawl stats afterwards
In Search Console Crawl stats, confirm requests shift away from parameter URLs over the following weeks.