Walking quickly (at a speed that you want to start jogging, but you don't) is less efficient for same distance than actually running..which is better for your h

Walking quickly (at a speed that you want to start jogging, but you don't) is less efficient for same distance than actually running..which is better for your health. To get the same benefits from running, you need to run faster/farther than walking. Just like when you switch biking, the same 3mi loop doesn't do any good and you need to start doing 10-15mi loops instead.