Just depends on how much wattage you want to burn in your wires. The thicker they are the less wattage they'll burn. The shorter they are the less wattage they'll burn. Also, the more wattage they burn (per ft; per m) the hotter they get (and more driver voltage they eat too), and too much heat melts solder and insulation ect. So ideally want to keep the waste wattage burned across the transmission wires low.
20awg is 0.01Ω/ft.
20awg waste watts per ft = amps² × 0.01Ω
* calculate total length, ie there AND back