Faceted Navigation & SEO
Faceted navigation is the set of filters in online shops that let users narrow product listings by attributes such as colour, size or price. Because every filter combination can technically generate its own URL, faceted navigation carries a high risk of duplicate content and a bloated crawl budget unless it is controlled carefully.
In practice
Usually only a selection of filter combinations with sufficient search volume ("red trainers size 42", for example) is released for indexing. For filter combinations you do not need, Google expressly recommends blocking crawling at the robots.txt level, because otherwise server load rises and new URLs are discovered more slowly; Google describes canonical tags as less effective for this purpose in the long run, and robots meta tags and parameter handling only govern indexing in any case. If you nevertheless keep filtered pages crawlable in order to preserve internal link equity, make that trade-off deliberately and watch the crawl volume in Search Console. Close coordination between the SEO and development teams is essential here, because filter logic is often configured centrally in the shop system.