To add a dose of reality...
If you are a sprinter, just about all of your training will be maximal. The variation will be in volume. The intensity will be maximum.
If you are an all-arounder or pursuiter, you'll have to train operating in "The Pain Cave", and that simply boils down to training against heart rate or RPE.
Having trained with power meters for years and logging so many workouts and races, power really just shows what the end result is of a lot of other upstream factors. For example, for pacing efforts, the heart controls how long power is applied, not the other way around. Watch the heart rate and you'll have a better idea as to how you are *currently* doing and whether you can turn it up a notch or turn it down. The Power being recorded is just the output of all of that, just like the speed or time of the effort.