Exercises 161 to 175 will focus on tactics that become possible by deflecting an obstructing piece to clear the way (the rank, file or diagonal) for your attacking piece. It’s important to note that the obstructing piece isn’t always an enemy piece, it could also be one of your own.
1… Rxd1+ 2. Nxd1 Re1#
The idea of the move 1… Rxd1+ is to clear the e-file for the rook on e8. In other words, the white knight is deflected from the e3-square–which clears the e-file for black’s rook.