Here is why I look up directions in advance in almost all situations:
* GPS is a distraction to maintaining awareness while driving, motorcycling, and bicycling.
* Navigational assistance does not help you when walking, taking public transit or taxis. Using GPS while driving prevents you from learning the layout of the place you are in which transfers to navigational competence for these other modes of transportation.
* You miss fun roads when following GPS navigation.
* GPS navigation is useless when planning long bicycle and motorcycle tours. I pick waypoints and routes between them in advance.
* GPS will route you into sketchy situations (like to phantom bridges) that you could have predicted by looking at a map.
* GPS does not take weather conditions into account when routing. People have gotten into floods (easy to see when looking at rivers and topo on a map in advance), stuck in snow, and have even died in the desert: http://www.sacbee.com/entertainment/living/travel/article257...
I do not know very many competent drivers who rely on GPS navigation. I see plenty of "GPS zombies" obliviously plowing through intersections and ignoring crosswalks every day.
The most use I get out of having a GPS dash unit is on trails and off-roading in my truck or motorcycle, where there is usually no signage for forest roads and trails.