Well, for one thing, when you draw off of a cut shot with a long, slow stroke, the CB does not diverge along the tangent line as far before it comes back. In essence, the softer you can hit the CB when drawing at an angle, the further back up table you can get it. The longer stroke is needed to get the distance required.
A long stroke with slow speed changes the forward speed/CB spin ratio, such that you lose most of the forward momentum whilst retaining a high rate of spin.
It is the same concept that allows Efren to do those inside english spin shots so effortlessly. When he is cutting a ball and wants to crawl the CB up the same rial, he puts inside english with draw, but he strokes softly with a long stroke.
The long stroke applies a lot of inside english, while the soft speed lets the cloth wear off the bottom english just as the CB arrives at the OB. Then, there is very little forward spin left, and a crapload of inside.
I think what makes Efren and the other Filipinos better at these types of strokes is that:
1. The have to shoot them all the time in Rotation
and
2. The practice a long stroke at all speeds, fast, medium, soft, and extra soft. And they know they effects of shortening the stroke inch by inch at each speed.
Russ