Do you have dead end sidings on your layout and have you ever driven a train off the end of the siding, crashing into the buffers or even worse, crashing through the buffers and off the layout and onto the floor thus ending in financial tragedy. If the answer to that question is yes then this is for you.
By having a single rail gap bridged by a diode correctly connected, an automatic dead section of a couple of feet may be inserted. Once the loco passes the gap, current is disconnected and the loco stops, somewhat abruptly but that is preferential to it ending up on the floor. To retrieve the loco from the siding simply reverse the line controller and the loco can be reversed out. This only works of course if the loco is at its traditional place at the front of the train.
Single diodes are also useful if headlights on locos are required to operate in one direction only. Just wire a diode in series with the lamp. If using LED lights make sure that reverse voltages are not connected across them. Use a regular diode in series with the LED.
Self flashing LED lights are available. If further regular LED lights are connected in series with one then all the LED lights in the circuit will flash, not just the flashing one. The uses are infinite.