They are great for group rides, even if your group is only 2.
On occasion I organize group rides of 10-20 riders, covering multiple days of 300+ miles each, sticking to twisty back roads. Preparation, distribution, and keeping folks from getting lost was a nightmare with paper maps. Reading a paper map is difficult while riding a long, complex route, and one can only memorize a limited number of turns.
With GPS, I carefully plan and test the route, then it's paint-by-numbers. The GPS tells the riders how long until the next turn, so they can rail until the last 1/4 mile before each intersection. Then follow the arrow and keep going until the next turn or stop. Impossible to get lost, the unit will re-route to the next rally point, lunch stop, or destination. No pulling over, no refolding the map, no trying to figure out how to get back on track. No worrying about missing a turn and having significant delays. No circling around trying to find cross streets on remote roads to get your bearings.
After the ride is over we archive the route and we now have a library stretching back years of well-planned, well-tested group ride routes.
When riding with just my g/f (on her own bike), she loves not having to worry about getting separated by traffic or speed, the GPS will keep her on our intended route. She won't feel the need to take risks to catch up. If she wants, she can point to our hotel and go directly there. A bonus: if we make a wrong turn or take a crazy road I can blame it on the GPS software...
Are there hiccups? Sure. And we carry paper as backup. But GPS has made group rides far more enjoyable for me. Our archive of routes and my personal library of waypoints is a hugely valuable resource for me too.
Solo trip to Alaska? Exploring on a lazy Sunday? The role of GPS is different....