For a start, we would all have to engage our brains and pay attention to the world around us when getting from A to B. Perhaps this would be no bad thing: we'd be less likely to drive into rivers or over cliffs through misplaced trust in our navigation devices.
Pick your own favourite story about the kind of idiocy only GPS can enable. Mine is the Swedish couple who misspelled the Italian island of Capri and turned up hundreds of miles away in Carpi, asking where the sea was.
But these are the exceptions.
Devices that use GPS usually stop us getting lost. If it failed, the roads would be clogged with drivers slowing to peer at signs or stopping to consult maps. If your commute involves a train, there'd be no information boards to tell you when to expect the next arrival.
Phone for a taxi, and you'd find a harassed operator trying to keep track of her fleet by calling the drivers. Open the Uber app, and - well, you get the picture.