When I started driving, I never knew people actually did this until I was with someone who did it off the highway. I personally come from the downshifting school of thought.
Several reasons:
1) You're in control of 100% of your car 100% off the time.
2) You're in the appropriate gear if you need to start moving again (rather then having to figure out which gear you need to be in)
3) If you need to make an evasive maneuver in the process, you can (refer to point #1).
Everyone has their own habits. I usually shift into neutral right around 10mph or when the car comes to a complete stop.
