Depends on the size of the pot (and how full said pot is).
Energy in - energy out == energy needed to boil.
If energy in per second is really high, and energy needed to boil is relatively small, you'll get there quickly, without energy out having time to have much effect. If the energy needed is very high, reducing the rate at which energy goes out can make a big difference.
alt Hacker News
Depends on the size of the pot (and how full said pot is).
Energy in - energy out == energy needed to boil.
If energy in per second is really high, and energy needed to boil is relatively small, you'll get there quickly, without energy out having time to have much effect. If the energy needed is very high, reducing the rate at which energy goes out can make a big difference.