It's very poor in emergency situations despite the slick marketing. There are homonyms and pluralisations which have led to rescuers going to nearby (but not near enough) locations when the 3 words have been misheard.

https://www.grough.co.uk/magazine/2022/08/31/dont-rely-solely-on-what3words-app-say-lakeland-rescuers-sent-to-wrong-side-of-lake

https://www.bbc.co.uk/news/technology-57156797.amp

https://nationalpost.com/news/world/what3words-app-has-been-sending-some-rescuers-to-wrong-locations/wcm/b6792fe7-dd3f-4776-8e1b-e67c0fb313de/amp/