Man! You guys are touchy!

I can certainly see where AWG can be critical and why electricians always seem upset when they're working in an old home where homeowners have added to circuits over the years.

I can see the senario where an old house has 2 or 3 bedrooms on one circuit with a couple plugs per bedroom. Owner 1 adds a couple more outlets per bedroom for convenience. Owner 2 makes one bedroom into an office and has multiple multi-plug cords to power the computer, printer, monitor, fans, space heater... No shorts, but the extra equipment now overloads the 15A circuit.

No problem. Just swap out the 15A breaker for a 20A. "It'll probably be okay". And in most cases, probably will considering the safety margins built into code.

Owner 2 has some issues and calls in the electrician who opens up boxes and finds AL wiring tied to copper plugs or wirenutted to copper for the new outlets, and the wirenuts are black from overheating and the box shows char.

I couldn't figure out why I had to run 12AWG thhn to fan circuits that I then spliced to 18 AWG vinyl coated at the appliance. I've realized through this series of posts that it's because people will add to the circuits, and that it's the fire inside the wall that you can't see that will kill you. That 18 AWG at the appliance will not have anything added to it.