If you hit the case I did, this will make your queries perform worse: The reason postgres insisted on table scan + sort was the random access time jumping around the disk and constantly invalidating the cache when it did an index scan. Using CLUSTER on the table made the index order match the table order so the index scan didn't jump around and there was no random access penalty - it instead worked with the disk cache.

If you're on an SSD and not a spinning disk, or have a lot of memory and can expect it to all be cached, there's a separate setting you can change to adjust the random access penalty - see random_page_cost on https://www.postgresql.org/docs/current/runtime-config-query...