Funnily enough the words "efficiently" and "bicycle touring" don't often go together in my vocabulary. I generally don't plan my routes in great detail, and some of my most enjoyable days on tour have resulted from my getting "lost" and seeing something I wouldn't otherwise have known about, or simply turning aside because I've spotted something, or a signpost to something, that interests me. If you plan your routes precisely and then simply follow the route you've uploaded to your garmin, then in my opinion you're missing a hell of a lot.

Paper maps are still an invaluable aid.