Speaker cable gauge and amplifier power

Based on my limited understanding of electricity, sending electricity through a wire is like sending water through a pipe. Using a larger cable gauge or bi-wiring will increase the amount of current required from the amplifier.

It seems like there must be a way to optimize speaker cable gauge and length based on an amp's current and watt ratings. Lower powered amps would mate best with narrower gauge speaker wire, and a powerful amp would benefit from thicker wire.

Am I oversimplifying, or are there established guidelines based on calculations of current, capacitance, etc.?