The rook is the second most powerful piece. Since they move on straight lines they need open ranks and files to be effective. Pushing or exchanging pawns to create open lines is usually the main way of getting the rooks into action.
The Rook’s strengths
Rooks are at their best when they can control open ranks and files. They are not only strong on open lines but they also give valuable support to the other pieces, in particular to the bishops and knights. In the endgame stage of the game rooks are also very useful in helping pawns to advance.
Examples of their strengths
In this example material is equal but white dominates the position since his rooks control the open files. White will play Rdd7 and get two rooks onto white’s 7th rank – and threaten Rxg7+