H. G. Muller wrote on Tue, Nov 8, 2016 07:50 AM UTC:
The value of an extra King might also be negative. I once tried the following test (requested by someone on chess.com): play a FIDE army without Queen against a FIDE army where the Queen was replaced by a second King, under rules of absolute royalty (i.e. none of the royals can be exposed to capture). The result was not significantly different from 50%. So on average the extra King is just as much a liability for getting mated as an asset for (defensive) tactics.
This is not equally distributed over the game, though. In a Pawn ending, a side with two Kings almost always beats a single King very easily. So in the late end-game the extra King is nearly as good as having an extra minor. That means that it should have a significantly negative value in the middle-game to neutralize its effect overall.
The value of an extra King might also be negative. I once tried the following test (requested by someone on chess.com): play a FIDE army without Queen against a FIDE army where the Queen was replaced by a second King, under rules of absolute royalty (i.e. none of the royals can be exposed to capture). The result was not significantly different from 50%. So on average the extra King is just as much a liability for getting mated as an asset for (defensive) tactics.
This is not equally distributed over the game, though. In a Pawn ending, a side with two Kings almost always beats a single King very easily. So in the late end-game the extra King is nearly as good as having an extra minor. That means that it should have a significantly negative value in the middle-game to neutralize its effect overall.