Examples

Sometimes a sacrifice is possible to remove other pieces that are shielding the king from attacks, for example the pawns shielding the king after castling.

White can sacrifice the queen with Qxh7+!
This removes the pawn h7, which was shielding the king from attacks on the h-file.
The decoy forces Black's reply Kxh7, after which White can checkmate with Rh4#.

Here a young Alexander Alekhine sacrificed his queen with Qxf1!
This removed the rook f1, which was shielding the king from attacks on the back-rank.
The decoy forced White's reply Kxf1, and also cleared the way for the rook, which could now checkmate with Rd1#.

Sometimes a decoy can even work without capturing anything:

White can win with the decoy Qh5+!
This forces the king to h5, and deflects it away from protecting h7.
After Kxh5, White can checkmate with Rh7#.

Related combinations

It is also possible to decoy a piece to a square where it can be attacked in a subsequent tactic.