I have one of those breadboards also. Because it has many bus strips, when laying out a large circuit using multiple voltages, I use a strict color coding regimen of black for ground, yellow for +12, blue for -12 and red for +5. These are the same color/voltage pairings used in computer power supplies. I mark the bus with a thin strip of matching colored striping tape from a hobby shop and use matching jumper wires for all connections to a bus. This may seem like a lot of trouble but it's worth it to avoid confusion and simplify troubleshooting on a busy breadboard.
The independent supplies can be connected together to create unusual voltage and polarity configurations such as a +12V and -12V for op amp circuits. Using just the two fixed supplies for example, you should be able to get 5, 7, 12 and 17 Volts.