I say this with respect to the creator of this video, the effort that went into it, and the potential value some viewers may receive from it.
I feel like this is an entry level approach to this topic. Nearly every beginner learns to memorize that specific scratch shot where you pocket a hanger in front of the side pocket from an angle and the cueball runs up to the corner pocket. As a beginner it's not bad to memorize that shot because it comes up a lot. Beginners end up learning to not shoot it or to shoot it soft. More skilled players control the cueball path with spin or cheat the pocket.
Once a player is trying to rise out of that beginner talent level, they need to build up some skills. I don't think memorizing more scratch shots from around the table is a particularly useful place to start. I don't think there's a lot of merit to this video as a piece of
reference material because in pool there's so much variability in real shots from the precise cut angle and positional demands. Rather than memorizing more scratch lines, I think the player needs to develop the skill to identify cueball paths from anywhere on the table and any cut angle. This video has more merit as a
training exercise to illustrate half ball hit paths using the pocket scratch as a target.
Another
training exercise approach to building that skill is this drill. You start with the cueball anywhere you want behind the 1-ball. Shoot a rolling cueball shot each time. Try to pocket the 1-ball and land the cueball in position 1 ten times. Then try to land in position 2 ten times. Don't try to accomplish it with different tip positions. Always use a high rolling ball. You accomplish it by changing your cueball position behind the 1. Once you land in position 2 ten times, move on to position 3, then 4, and so on. (drawing was rushed on a phone so exact ball positions are a bit rough-sketch)
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You work on this drill and your brain now starts to "see" the cueball path from any position on the table without needing a peace sign and without needing to memorize a catalog of specific shots. And this drill can be repeated from different positions on the table with different targets as needed (cutting to the left and to the right) if you really want to feed your brain with target-expectation-result scenarios. The only shots I tend to memorize as scratches are common ones involving one or more rails.