Index a faceted URL when it maps to real search demand, and block or noindex the combinatorial explosion of low-demand combinations that only create crawl waste and duplication. The pivot is whether the facet has its own demand: does a meaningful number of people actually search for that filtered view as a thing in itself? Neither pole, “index all facets” nor “block all facets,” gets this right, because facets are not uniform. Some are valuable landing pages in disguise, and most are noise, so the decision has to run filter by filter rather than as one switch.
The facets worth indexing are the ones that match how people search. A single attribute filter that aligns with a real query, a popular size, a color people shop by name, a recognized brand within a category, can be a legitimate destination that captures specific intent. When the filtered URL corresponds to a query with genuine volume and the page it produces is coherent and useful, indexing it lets you rank for that intent rather than forcing everything through the broad category. These are few, and you can usually name them.
The facets to block are the combinatorial rest, and this is where catalogs drown. Once filters stack, color plus size plus price range plus rating plus sort order, the number of possible URLs explodes into the thousands or millions, almost none of which anyone searches for. Each one is a near-duplicate of the category, splitting signals, wasting crawl budget on pages that will never rank, and bloating the index with thin variants. Blocking or noindexing these protects the pages that matter from being lost in the noise.
The reason this matters is that crawl attention and index space are finite. Letting the engine wander an infinite facet space means it spends its time on duplicates instead of your real products and key landing pages, and the duplication can drag on overall quality signals. Controlling what is crawlable and indexable keeps that attention pointed at the URLs you actually want to win.
To apply this, list the filters your shoppers genuinely search for and make those specific facet URLs cleanly indexable, then block or noindex the combinatorial stacking and the long tail of low-demand combinations. Index the demand-backed facets, contain the rest, and let your crawl budget land where it earns its keep.