Don't forget that the performance improvement of hash over b-tree gets better for wide keys - the wider the key, the better the improvement, as the key width is irrelevant to the hash index.
Based on the width of the key, the row count and the amount of memory available, there might be instances where a disk-hit gets replaced with an in-memory cache, which is awesome for spinning-disk based systems.
Good point, I think it would be nice to add it to the docs.
Maybe with part numbers of goods as an example - in typical OLTP DB they are variable width strings, mostly read-heavy, unique (not as constraint but as the matter of fact) and searched by almost constantly.
Based on the width of the key, the row count and the amount of memory available, there might be instances where a disk-hit gets replaced with an in-memory cache, which is awesome for spinning-disk based systems.