There is very little chance of overloading a 15 amp circuit when using 4/0 ser cable for the branch circuit wiring. Its just hard to get the receptacles into the box afterwards. Seriously, you can overload a 20 amp circuit wired with #12 just as easy as you can a 15 amp circuit wired with #14. But I still prefer to wire all receptacles with #12, just since they make some high powered vacume cleaners nowadays. Lighting circuits in a residential - #14 is my standard. On commercial there is a fair chance of somebody adding drop in fixtures to the existing circuits, so I use lots of circuits and minimum #12 branch, lots of times #10 branch wiring for the lights on a 20 amp breaker.