The following middle game from a match of two masters furnishes an example.  After White’s seventh move the position of Diagram 49 was reached, in which Black continued with P-b5 with the view to playing B-g4 and Kt-d4.  White replied (8) B-b3, B-g4; (9) Kt-e2.  Better would surely have been B-e3, which develops a new piece.  To allow the exchange of f3 which forces the g-Pawn out is dangerous because Black may castle on the Queen’s side and storm with the Pawns of his King’s wing.

+---------------------------------------+
8 | #R |    | #B | #Q | #K |    |    | #R |
|---------------------------------------|
7 |    | #P | #P |    |    | #P | #P | #P |
|---------------------------------------|
6 | #P |    | #Kt| #P |    | #Kt|    |    |
|---------------------------------------|
5 |    |    | #B |    | #P |    |    |    |
|---------------------------------------|
4 | ^B |    |    |    | ^P |    |    |    |
|---------------------------------------|
3 |    |    | ^Kt| ^P |    | ^Kt|    |    |
|---------------------------------------|
2 | ^P | ^P | ^P |    |    | ^P | ^P | ^P |
|---------------------------------------|
1 | ^R |    | ^B | ^Q |    | ^R | ^K |    |
+---------------------------------------+
a    b    c    d    e    f    g    h

Diagram 49.

From Black’s next move, Q-d7, it is indeed apparent that he has decided on a maneuver of this kind.  The game continued:  (10) P-c3, Bxf3; (11) Pxf3, Q-h3; (12) Kt-g3, P-h5; (13) B-e3.  He cannot play R-e1 on account of Bxf2+ followed by Qxh2+ and Qxg3. (13) ..., P-h4; (14) Kt-h1, R-h6 and wins, for if White takes the Rook, Pxh6 opens the g-file and the other Rook occupies it with deadly effect.

In the last example it was easy for the Rooks to take an active part in the battle because a file was open which enabled them to bear down on the opposing King.

+---------------------------------------+
8 | #R |    | #B | #Q |    | #R | #K |    |
|---------------------------------------|
7 |    | #P |    | #P | #Kt| #P | #B | #P |
|---------------------------------------|
6 | #P |    | #Kt|    | #P |    | #P |    |
|---------------------------------------|
5 |    |    | #P |    |    |    | ^B |    |
|---------------------------------------|
4 |    |    | ^B |    | ^P |    |    |    |
|---------------------------------------|
3 |    |    | ^Kt| ^P |    | ^Kt|    |    |
|---------------------------------------|
2 | ^P | ^P | ^P | ^Q |    | ^P | ^P | ^P |
|---------------------------------------|
1 |    |    | ^K | ^R |    |    |    | ^R |
+---------------------------------------+
a    b    c    d    e    f    g    h

Diagram 50.