Space (HTRYC 3rd)

Space, as defined by Silman, is the "player's territory usually determined by the positioning of one's pawns."  It's the area of property behind the pawns.

The reason it's important: if you have more territory, you also possess more room in which to move around.

1. the side with less space should initiate exchanges so that he will have more room in which to move around.
2. alternatively, the side with more space should avoid exchanges and instead focus on increasing the space advantage.

However, there is a "dark side of space"

1. the further a pawn advances the less space it can potentially control

Other rules

1. in closed positions with locked centers you must attempt to get open lines on the wings by breaking with pawns