ironDigit
this link might help
http://www.csgnetwork.com/voltagedropcalc.html
It is a nice calculator. If you play with it you can see the effects of different conductors on voltage drop. Voltage drop is bad. Voltage drop is caused by the resistance in the wire. See the tables above.
The power is lost as wattage (volts drop*amps). If you have lots of voltage drop from resistance and distance you are turning the wire into a heater - this is bad. The table and pdf above show you the values to plug into formulas or use can use this calculator.
Use the right size wire and you don't have a heater that might create a fire. You also don't pay for electricity that you aren't using. Don't go too big on the wire or you will pay a ton of money for the wire.
maybe this helps