For me if I want to avoid tiresome detours & backtracking then well, GPS is an absolute necessity. Usually I write a cue sheet while looking at PC maps but sometimes the intersections look different in person. W/O GPS I'd have to budget in extra time for wrong turns. While motor-touring I've occasionally seen some interesting things while "winging" it but on bike rides not so much; can be dispiriting to have to ride 15 km extra on an already-challenging day.