As with everything, it depends. If you are going to do the same jobs regardless of the amount of time it takes, then yeah, dropping the max power probably just spreads the energy use over time. That doesn't usually help you save money, unless you have a very interesting residential plan.

OTOH, if it's something like realtime game rendering without a frame limiter, throttling would reduce the frame rate, reducing the total amount of work done, and most likely the total energy expended.