The suggestion in the book was that really Grandmasters have spent so much time practicing, that they have memorized the game and the board to a certain extant that allows them to more easily handle the board and all the pieces on it cognitively.
Because of this sort of advice ppl equate memorization with "not understanding" and cramming.
Never memorize things you don't understand.
Memorization is important and understanding is important, and the two are not in any conflict whatsoever.
Chess and math are regular domains. They are bounded. There is right and wrong. Most domains are not like this. Ex: art, software engineering, investing, etc.
You can't memorize your way to understanding in an irregular domain. It also doesn't tend to do well in non-knowledge work domains. Ex: sports.
For sports rote repetition is basis to excel or at least getting good at any sport.
I agree one cannot "memorize to understanding" because one has to actually apply what he memorized in practice.
To really understand something first you blindly memorize - but that is not enough, once you do examples and exercises using what you blindly memorized you get to understand things quicker, a lot quicker.
Not memorizing stuff and figuring things as you go is mostly recipe for disappointment.
Like in chess - people think that chess players are somehow super intelligent - but being super intelligent without rote memorization of loads of chess settings will not help winning grand master title.