The limiting capacity of an extension cord is the resistance it can carry - at high resistance the cord will basically catch on fire. High voltage can deliver much more power at lower resistance as compared to low voltage. The easy example is household power -- in the US, standard household electricity is 120v, so a common 14 gauge wire that can carry 12A at constant load would be able to deliver 1400 watts. If you use 240v, that same wire can deliver 2800 watts.

To extend that to extension cords -- if your boat/tool or whatever needs 5kw of power, at household voltage of 120v, you'd need a #4 wire which weighs 1.3 lbs/10 ft. At 240V, you'd need a #10 wire which weighs 0.3 lbs/10 ft. At 360v, only a #14 wire which weighs 0.13 lbs/10 ft.

So by tripling the voltage, you can cut down the weight of the cable by roughly 10x.

Thanks for the detailed reply, I really appreciate it! Now to go down the rabbit hole a bit more...

Basically, conductor weight is proportional to the current, while insulator weight is proportional to the voltage.

It turns out that our insulators are much more efficient than our conductors, so the trade-off is a non-brainier up to extremely high voltages.