Gully makes a very good point...you are not only keeping the edge by keeping it cool, you are keeping the hardness where it was tempered to begin with. If you heat the edge to much it will change the hardness of the bit, sometimes to the point to where it will not even hold an edge.
Learning to sharpen a drill bit by hand is an art. Its something people do not do anymore and its really a shame. I teach my kids in welding class to do it, then let them try to drill with it. I won't let them be done until they can drill through a piece of 3/8" mild steel...oh the attitudes you get...lol, but when they get through...wow, they are so proud. Then I show them the drill doctor...lol. Most people do not realize there are so many parts to a drill bit...look it up in google images sometime, they are pretty complex for what they are.