The squares in “What three words” are just 3m x 3 m in size.
A six figure O S grid reference is 100m x 100m
Having just had to use a post code in rural Exmoor to locate a site, the “What 3 Words” would have made it a lot simpler

 
If I'm lost in the coutryside ... if I'm not sure where I am, or need emergency help, I can identify my location to let people know using the "what 3 words" app on my phone.  Three words identify me down to a 3 metre x 3 metre square on a grid, and the emergency services and perhaps my frineds and contacts and perhaps even taxi services are starting to pick the system up. So if I'm standing at what looks like a shuttle turning circle but there are no shuttles at  ///crumples.amuse.origin, I can cal for help.  If I wander off down the road from there I can re-identify to ///wobbling.saundas.playfully or  ///native.jubilant.ambition ... if I have wandered futher to a dour industry / business area at ///blueberry.repeats.pronouns I can identify that to people too.

So what does this system have over Latitude / longitude, over OS Grid reference, or over postcodes?  Well - postcodes are for habitation and businesses where post may go, and are lacking in the countryside.  Latitude and longitude are base 10 (digit) based and have fare more significnat elements than "what 3 words" which can more easily (discuss) be wrongly relayed.  On the other hand, there are concerns that "what 3 words" is in the hands of a single commercial company.  The algorithm is not obvious so that squares bordering each other have no linking pattern, and just sometimes the phrases that it brings up may not feel quite appropriate.  Had I known early on that ///hypocrite.thinking.possible would become an important location to me, I might have seen it as an ill omen.  On the other hand, I don't mind shletering at ///amount.pies.toothpick, though having eaten an amount of pies there I can't help wondering what was in them for me to need toothpicks!

Some more places to try ... ///smiled.human.domain ///sushi.king.bank ///limitless.descended.nesting ///winemaker.shout.deflated ///marked.space.change ///erase.blur.sorry or ///mash.form.torch or ///event.half.milk ///limitless.descended.nesting nd ///winemaker.shout.deflated

Finally, do you remember the film "Notting Hill" where Julia Roberts tells Hugh Grant to come on up?  She used the codename Pocohantas, for had she told Hugh to come up to ///agenda.fancy.sprint, the poor sod whould stll have been at a loss to know which floor.