What is the elo value of memorizing book moves based on an engine?

[Uri Blass]

Many engines in lichess have fairly wide opening books, and will play some offbeat lines. So if the move is coming from their book it may not be the best choice. It doesn't matter for engines because most are using Stockfish, which is so strong it can overcome an opening disadvantage. But if you are learning from them, you should realize that their book moves may not be as strong as moves that come from search.

The idea is to memorize opening moves that come from search so books of engines are not relevant.

[Uri Blass]

If you randomly memorise lines which have no relation to one another, there is precisely zero Elo added to a human's chess IMO.

On the other hand, if you have you already have a basic opening repertoire, and make it bulletproof by "fixing" lines with modern engine improvements in certain positions, this can be big.

I've seen estimates as high as +150 Elo for having a full no holes repertoire.

In fact, I've manufactured such results when training some of the kids I coach.

One 8 year old boy in China switched from 1...e5 to Caro Kann, learned the lines I taught him (sharpened with SF, and Patricia as backup) and went from 1500-1880 Rapid on liChess.

Such training really needs to be done properly though.

As Graham says, there needs to be underlying *understanding* of the opening structures, plans, tricks etc as well.

I agree that randomly memorizing lines is not the best idea but I am not sure it gives 0 elo.
If the lines are objectively good you get the following advantages:
1)time advantage on the clock relative to your opponent.
2)A better position out of book.

A possible disadvantage may be that you do not know how to play the position you get out of book but it is not that you play against GM's and there is a good chance that your opponent also will not know how to play the position.

Note that when I memorize I try to understand and in part of the cases I clearly have a reason that I understand for choosing a move(not in all cases but the idea is that if I do not understand and make a mistake later I am going to increase the size of the book to correct the mistake in future games.

In theory with a book that is big enough I can play perfect chess but of course there is a limitation for my memory.