One benefit or goal I have not seen mentioned is fat burining. A steady, long, very mildly aerobic workout at about 65% of maximum heart rate will call on energy stored as fat to a greater degree. Higher intensity activity will derive more from glycogen stores and carbs. Losing fat is a laudable health goal in my opinion. Coupled with moderate strength training to build and firm muscle tissue is also a laudable health goal.
One eventually wears out on long slow rides. One wears out on short intense rides. One wears out on tough hill climbs. One wears out eventually when doing high rep - low weight strength training or heavy lifting. Any of this "wear and tear" can eventually lead to varying levels of discomfort and even pain. As others have said though, it is all really goal dependent.
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Just Peddlin' Around