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http://www.chess.com/forum/view/general/what-is-the-value-of-the-king
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http://www.chess.com/forum/view/chess960-chess-variants/establishing-the-value-of-a-chess-piece
if the king was just a normal piece what would you say it's worth?

A knight and a pawn or roughly 4 points. The king's strength is in the endgame where it's a fighting piece as opposed to a hiding piece.

Definition: A man (german: Mann) is a fairy chess piece often used in chess variants. It moves like a king, but is not otherwise treated as one (i.e., it has no royal power).[1]
A man is approximately equal in strength and value to a knight, generally. Often it takes a few moves to get the man properly developed in the opening. It is effective at close proximity, where its striking power is considerable. Although it is rather slow, the man is excellent at both attacking and defending nearby pieces and pawns, similar to the king (Ward 1996:13). The man reaches its peak strength during the endgame, in which its value is slightly more than a knight, despite being slightly less than a knight in the opening.[3]
A man is definitely stronger than knight. King + man do checkmate opponent's king, king + knight don't. Man near own king in the corner creates unpenetrable defence and draws vs queen, knight always loses. Man can create/handle zugzwang by triangle movement, knight can't.
the king as we know has to be protected from checkmate and thus can't be used as a normal piece however what if it was. there are things we need to consider with the king having it's freedom.
first kings being adjacent to each other.
this is important because we need to see how an exchange of kings effects the game. (two kings would only be touching each other if another piece was defending so king takes king defending piece takes king). but in order to know this we need to know the value of the kings don't we? in fact not necessarily. because it takes four moves for both kings (assuming no pieces are in the way.) to be touching. this time could easily be spent developing pieces in the opening and trying to create an attack in the middle game which means this scenario is most likely in the late-middle game to endgame. we know that the king is very good at helping promoting pawns so this would most likely lead to a draw. but because it takes four moves of both kings reaching the centre it's more likely to be a defensive piece unlike all other pieces which can do both. this could potentially lessen the value.
secondly castling.
if the absence of checking and checkmating being the only difference then why castle? well there is reason which gives castling some merit. this is developing the rooks. getting them involved. in the game but this makes it more difficult to develop the king which is hard enough to develop as it is. but not doing so makes it slightly harder to get the rooks involved which are probably more valuable than the value we'll give the king. however it's probably easier to get un-castled rooks involved than a castled king involved which will be an interesting dilemma the player will have to think about.
finally: what is the goal of the game?
this is a difficult one however i suggest (if someone comes up with a better one i will edit my comment.) the first player to promote a pawn without the opponent doing so immediately after/can't be taken immediately after. This will make the king more useful but not as useful as the normal rules.
my personal verdict :
king value = 1 (equivalent to a pawn).
because of the difficulty of developing the king then it's not hugely useful in the middle game at the time it is developed i struggle to find strong points of this piece. i'd rate it worse than a pawn if it didn't have any use in the endgame.
what do you think? have i been too harsh or missed out anything or even was incorrect on any of my points?