I understand the use for two binding posts on a breadboard: namely to connect the + and - of a DC power supply. But what it the purpose of breadboards with three binding posts?
In this tutorial I read: "Typically, you only need to connect a power and ground wire from the posts to the breadboard. If you need an alternate power source, you can use the third post." But would I not need a third and fourth binding post to connect a second power supply?
So how do you make use of just a third binding post?