Digits have ten words. If five and nine are confusing, imagine trying to guess if the person meant flower, flour or floor, and guessing according to their accent.
If one to ten is confusing, you can always find 10 or 100 very distinct words to replace digits or pairs of them. You could also press numbers on your phone's keypad, or even send them as morse or binary.
I'd hope that w3w's word list is built to avoid this potential confusion, but I could be wrong.
> you can always find 10 or 100 very distinct words to replace digits or pairs of them
True, although if you wanted to spread news by word of mouth of a secret gathering in the woods, then having just three words for the location is easy to remember and transmit.
Beyond those very niche edge cases, I don't really see much point.
I can't think of many use cases where w3w would be more convenient than an app/protocol for simply transmitting your GPS location to another person. Maybe if you had a GPS connection and mobile signal but no internet connection.