I suppose it depends on your goals. I can be quite happy just riding around, exploring the area, stopping often and having fun. Especially if I ride different areas from time to time. You can achieve moderate fitness and health without really trying.
OTOH if your goal to get in really good shape fitness and health or to ride better then training is good. I've skimmed Friel's book on cycling past 50 and the time crunched book as well. My problem is I'm too cheap. Not going to buy a power meter nor heart rate or cadence monitor.