In this case, the single common line has 8 selectable paths and therefore it can be used to extend a single digital or analog input/output to 8 different devices. To control which of the 8 paths is connected to the common pin, a series of control lines are set HIGH/LOW.

These are ideal for microcontrollers / single board computers where there are limited pins available, but a lot of different control options / read options are required. In the case of limited numbers of pins with special functionality (interrupts, analog input / output, etc.) this can be expanded using a multiplexer instead of moving to a more complex controller.