I am trying to improve my billiards playing. I have found a similar approach. I aim at a spot on the target ball. I stroke slowly enough so I can clearly see the collision. I then evaluate - did I hit my mark? Was I left or right? Why?
On guitar, I am trying to learn some acoustic blues in DADGAD tuning. This is new enough to me that I am forced to slow down. But I think the same approach needs to be taken - have an intention, execute, evaluate how close you came to your intention, and adjust.
One thing that I have found helpful in learning a difficult piece is to (a) learn it backwards, from the final measure back to the front, and (b) only work on a measure or two for a half hour. At the end of the half hour practice, I play through to the end a few times, at slow tempo. So by the time I am fully though the piece, I have practice each measure hundreds, maybe thousands of times, and I have played the end more than the beginning.
This also helps in avoiding the temptation to try to play the whole piece through, slow or not, until I'm ready.
On a related aside, I had a teacher once recommend taking a piece that you can play and playing it as LOUD as possible, on every beat. Then play it softly. That sets the parameters for dynamics. Now go back and work on those dynamics, again with intention/execution/evaluation/correction
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