[Al Skierkiewicz]

Oz,
As Andy has pointed out, extra wire can be a problem for many reasons. In most cases when this question comes up, teams are asking about motor wiring. Although the rules allow for #12, I don't recommend it. #10 is a nice wire to use and has about .001 ohm per foot. Most of our motors are running close to 100 amps stall current and so a quick calculation will tell you a #10 will drop 0.1 volt per foot under these conditions. Make the wiring two feet longer than needed adds 4 feet of wire (red and black both are part of the circuit, remember.) or drops 0.4 volts in addition to all the other losses. When motor ops are important (when are they not?) I would rather have the 0.4 volts supplied to the motor instead of heating up the wire.
As to coding the wiring, this is what we do. Digikey sells a 3M color tape dispenser. (It is expensive for what it is but it has 10 colors on it.) We color code everything on our robot. A single circuit will have a colored tape on each wire, circuit breaker, position on the power panel, speed controller, PMW cables, PWM output on the RC, motor and motor position. That way if the "yellow" motor is out of control, you pull the yellow circuit breaker and it stops. You can tell by looking that the "yellow" circuit breaker goes back into position 2 because there is a "yellow" tape marking the breaker panel. You know it was the "yellow" motor because there is tape on it and there is yellow tape next to it's mounting position on the robot so when it is pulled out, you know which motor is missing. When the motor isn't running, you look at the "yellow" speed controller to see if the fan is running. (We tape the fan so it's spins a pretty color.) If the fan is running you look to the RC to see if the "yellow" PWM has pulled out.