How faceted filters work
A category page shows a set of products. Faceted filters let the shopper narrow that set by attributes held against each item — brand, size, colour, material, price band, availability. Each attribute is a facet, and each choice within it is a value. Ticking two boxes narrows the list twice.
What matters technically is what happens to the address bar. Most shops express the selection in the URL, usually as parameters appended to the category path, so that a filtered view can be shared or bookmarked. That is convenient for shoppers and it is where the trouble starts, because every combination of every value produces a distinct address that a crawler can find and follow.
Why faceted filters matter
For shoppers they are the difference between browsing and finding. A visitor who wants running shoes in one size and one price band should not have to scroll a long listing, and a shop that makes that easy converts better than one that does not.
For search there is genuine opportunity in a small number of those combinations. People do search for a brand within a category, or a colour within a product type, and a filtered view that matches such a search can be a strong landing page. The skill is deciding which handful deserve to exist as real, indexable pages and treating the rest as a shopper convenience only.
Where faceted filters go wrong
Left unmanaged, they multiply. A category with several facets generates far more filtered addresses than it has products, most of them showing near-identical or empty results. Crawlers wander through that space, spending their attention on views nobody searches for while genuinely important pages wait, and the index fills with thin duplicates of the same listing.
Sort order makes it worse. Sorting by price and by popularity returns the same products in a different order, yet each often carries its own URL, so the same set of items is published repeatedly under different addresses.
The final problem is that these pages compete with each other and with the plain category page for the same query, so no single version accumulates the signals it needs. Managing crawl budget is the polite name for stopping this.
How to act on it
Decide deliberately which filtered views earn a real page. Pick the combinations with genuine search demand, usually a single facet such as brand or colour within a category, give them clean addresses and unique introductory copy, and let them be indexed and linked.
Everything else should be reachable by shoppers but not treated as a page in its own right: keep those combinations out of the crawl path, avoid linking to them from navigation, and make sure sort orders and pagination do not create additional versions of the same listing. Getting this right is a technical SEO decision made once and enforced by the template, not something to clean up page by page later.