3 | | | | | | | ^B | | |---------------------------------------| 2 | ^P | ^P | | | | | ^P | ^P | |---------------------------------------| 1 | ^R | | | ^R | | | ^K | | +---------------------------------------+ a b c d e f g h

Diagram 38.

The way in which White would obtain the advantage is this: 

(1) R-e1 B-f5
(2) Rxe4 Bxe4
(3) R-e1

Through sacrificing one Rook for the Knight White has freed the square e1 for the other Rook who now pins the Black Bishop without Black being able to protect it.

The position of Diagram 39 is somewhat related to that of Diagram 38, as far as the possibility of a sacrifice for the sake of a pin is concerned.  If White plays B-b5+ Black must not interpose his Bishop, for White will give up his Rook for the Bishop in order to force the Rook d8 into a pinned position and then he will win the Rook by R-d1.

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

Diagram 39.

In the position of Diagram 40 there is also a possibility of a sacrifice with the view to pin a piece that defends a certain threat as long as it is mobile.  White plays (1) Q-d5, and Black dares not take White’s Knight with his Queen for White would continue (2) Qxf7+, Rxf7; (3) R-e8+/-.

What Black could try is (1) Kt-h6.

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

Diagram 40.