At the Cleansing it was revealed that the likes of Demandred and Cyndane could make new gateways immediately after arriving at the Battle Zone. This defied the existing explanation that you had to spend time getting to know a place before you could make gateways from it.

Personally, I think RJ saw the tactical need to be able to make a lot of gateways quickly in the heat of battle, so he had to change the rule somewhat to explain how this is possible.

Pretty soon after Winter's Heart, if I recall correctly, Rand suddenly mentions that you don't have to know a place to make gateways for short distances (i.e. to destinations in close proximity to the first gateway.) Now this goes against the explanation we had before, as making a gateway does not mean you have to know your destination, but that you have to know where you're Travelling from.

In any case, Rand now makes gateways to places within the same city with no problem. This despite the fact that Skimming was used for such short distance Travelling in the past.

But now, RJ had another problem. The implication of making a gateway FROM somewhere, however short it might be, is that you now KNOW that place. Certainly, when using saidar you make your destination similar to your departure point.

So the net result is that once you've made a gateway from a place, even if it is for a short distance, then you KNOW that part of the Pattern.

In tGS, Nynaeve observes Rand making use of this principle. When he doesn't know a place well enough to Travel from it, he simply makes a "short" gateway to somewhere close by - which now is possible as per Demandred and Cyndane at the Cleansing.

Then he immediately closes this "short" gateway, without actually using it. The purpose of this exercise was to familiarize himself with the area. So now he is able to make a "long" gateway, to anywhere he chooses to go.

The net effect is that he no longer has to wait and familiarize himself with an area. Instead, by using this trick he can Travel anywhere at any time.

The whole of the above obviously begs the question: "Why didn't Asmodean just teach him this trick instead of going into the long explanation of why Skimming is necessary if you know your destination but not your departure point.

And why did Asmodean use Skimming to get to Rhuidean, and not just this much quicker trick, which would have handed him the Choedan Kal without any interference from Rand. In hindsight of course.