Well if a person would do this over most of their working career (35 years) they could help themselves out significantly as it turns out. I live only 2 miles away so a round trip consumes 140 calories. In constant dollar terms it saves me $2.60 per trip vs driving my truck. I also save 0.2 tons of carbon pollution per year.
While this may not sound like much, let's examine it from a longer term perspective and you'll begin to see why people in other countries are able to save more money and also have smaller waist lines. If you're currently in your mid-30s and you want to start doing this let me know you how much this will help you.
Over the next 30 years you will burn an extra 240,000 calories, which conservatively equates to 70 pounds of fat. How much have you gained since you started working? You'll also save almost $18,000 by the time you reach 65. This is adjusted for inflation, so the actual amount that you'll see will be even higher. You'll also save 4.6 tons worth of carbon, which equates to about half a years worth of driving for the average American.
If you don't know what any of this means, here it is in basic English: get off your fat ass and run some daily errands via your bike!