A space advantage means your pawns and pieces control more of the board than the opponent’s, giving your pieces more room to manoeuvre while theirs stay cramped.
Space is usually measured by how far your pawns have advanced: pawns on the 4th, 5th or 6th rank stake out territory behind which your pieces can shuffle freely, while the opponent’s pieces are crowded into a smaller area.
The practical benefit is mobility. With more room you can switch the point of attack from one wing to the other faster than the defender can react, and their pieces often get in each other’s way in the cramped space.
Space comes with a warning: advanced pawns can no longer defend the squares behind them, so overextending can leave holes and targets. The classic advice for the cramped side is to trade pieces — fewer pieces need less room.
Generally it helps, because your pieces have more room than the opponent’s. But advanced pawns leave weak squares behind them, so overextended space can become a liability.
Trade pieces — the cramped side suffers most from a lack of room, so swapping pieces eases the congestion and can leave the over-extended pawns as targets.
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