Guidebooks and maps are essential tools for the world wanderer. Impulsive decisions are great, but you still need to know how to get where you're going and where to stay once you've arrived. I'm a map freak. Nelles is important for some parts of the world. Other brands, tourist office maps, government maps, survey sheets, and atlases all have their advantages.
Maps are perhaps more important for threading than for other approaches to travel.
The city-hopper can use a rough map to decide that Luxembourg City will follow Dusseldorf and work out the rest with a train schedule and guidebook. The threader taking three days for the same trip will want a map that shows rail lines, back roads, footpaths, historic sites, hostel locations, water sources, refuges, etc. When you see a dotted line that winds past a symbol for megalithic ruins, you're tempted to hit the trail and see for yourself. You have to have them. At least, most of us in most circumstances will want guidebooks along to support our efforts.