I never heard of this rule, but its a good rule, thanks for that!
a similar rule I found myself and read it nowhere: The knight is the best defender. If you are under attack and need to get a piece closer to your king, the knight is usually the best defender.
Other way round: if you consider an exchange sac, you want it to do against the knight (as it is the strongest defender).
Also, if there are 2 knights nearby to defend, you can look at concrete sac-possiblities, but not for too long - usually it is not worth it, 2 knights are just too strong defenders.
Another rule: for white aim for symetrical openings, for black seek assymetry.
Examples: 1.e4 e5 2.Nf3 Nf6 is statistically poor for black, whereas 1.e4 c5 is statistically quite good for black.
Another rule: if black plays in the opening ...e6, then the statistically most promissing reply is g2-g3 and fianchetto the Bishop on g2.
Or this one: an early ....Nf6 development is statistically poor, because it is often the target of attacks.
Example: 1.e4 e5 2.Nf3 Nf6(?) or the modern is much more promissing than the pirc. In the modern you delay the ....Nf6 development. Thus, strictly speaking, this is a poor approach, too (indian opening): 1.Nf3 Nf6(?) 2.c4! - why? because the black knight would want to jump to e4, but the d-pawn has not been played yet, so d2-d3 would attack a knight on e4. A few moves later you can move d2-d4.
in the KID black likes to attack a white pawn on e4. Avoid giving him this target. Either delay e2-e4 by playing e2-e3 first and consolidate, or play g2-g3 and Bg2 and do not place a pawn on e4 at all.
Many players might argue with these rules. However, if you look at various openings and their statstics, you will see, it is all true!
Very good tip
A lesson from Larry D Evans from ages ago: the queen is a lousy defender. But always look at the board because “ chess is concrete game” ( say it with a Russian accent).
I have heard this too, IRL from a Swedish GM (Lars Karlsson), even if phrased like "it is more economic to defend with a less valuable piece". I have not read it, but I would be extremely surprised if no famous book mentions it.
In the second position though, I wouldve regarded the overall danger as huge and I wouldve tried to trade queens w Qf3 Qf5 before f3 (and lost)
Exception to the rule: the king can block the opponent free passer better than a rook. However, a king is worth the whole game, whereas you can lose a rook and still play on.
But joking aside, a king has about the same power like a knight or bishop or a king can block 3 connected pawns (if they are not too advanced).
The rule of thumb is that generally you better move pieces up than backwards