Geohashes are incredibly useful when building geospatial software (at least at the UI layer or close to it). With them, bucketing multiple data points that are in close proximity to each other is a breeze, and you then do zooming, panning, etc. with those buckets.
W3W (or the better alternative of Plus Codes) is then essentially just a layer of human readable names to have a digestible encoding of geohashes.
Also, if you are set on using a geocode system, geohashes and plus codes are open-source, public-domain algorithms, unlike w3w, to avoid issues like [1] which was being discussed on HN yesterday.
A geohash is 6ish characters and coordinates are usually 10-15 digits. They are both pretty short either way, but a people can remember/communicate 6 characters way easier than 10-15.
W3W (or the better alternative of Plus Codes) is then essentially just a layer of human readable names to have a digestible encoding of geohashes.