It often happens that a piece may protect two or more objectives at the same time. When this happens we refer to that piece as being overloaded. Usually, when your opponent has an overloaded piece you can use it in your favor by performing powerful attacks on his position (more exactly on the overloaded piece).
Look at the example below. You can see that the white queen protects the white rook from a4 and the knight from e4. Black tries to take advantage of this by attacking the queen 1... Ra8-c8 but White can easily defend with 2. Ne4-c3. With this White stopped the rook's range of action and got the knight from the exposed square e4. This proves that attacking an overloaded piece (and generally using any other tactical procedure) won't always bring you the advantage if your opponent has enough resources to protect himself. This was an example of how you can protect your position against certain attacks of this kind.