I guess you could run your errands running but I guess brisk walking could be easier to incorporate for most in their routine, especially for non runners. Besides, running with the wrong form could do more damage than walking.

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.

running is hard on joints, esp for heavier folks.

That depends of your weight and testosteron level because the body fights the inflammation by producing cortisol.