Say in a 20 mile commute, 14 miles is on the highway with a speed limit of 65mph, 3 miles is on a road with a speed limit of 45mph, and 3 miles is on a residential road with a speed limit of 35mph. Furthermore, to simplify this, let's say you only speed on the highway. Going 65mph will result in 12.9 minutes on the highway, going 80mph will result in 10.5 minutes on the highway. By speeding, you exposed yourself to financial risk, and yourself and others to physical risk in order to save 2.4 minutes.
Now, let's say you encounter 6 stop lights on your commute, each with an average red light time of 1 minute. Let's say on average, you get caught in half of them each time you make the trip and that there are no backups requiring you to stay at any given light for more than 1 cycle. So your average red light time per commute is 3 minutes.
You've now spent more time waiting at red lights than you have saved by speeding on your commute.
On long trips, speeding can save you hours instead of minutes, so it seems more justified. But for a savings of 2.5 minutes that can easily be negated by red lights or other drivers? Why put yourself and others at risk for such a small reward?