I originally had the term "power principle" in my head, but googling around makes it seem like it's not actually a common phrase and may be one I made up. Essentially, I'd like to say "do the things that will give you a lot of impact with little effort."
There is a principle that has a similar connotation, to the one you have talked about in your question:
The Pareto principle (also known as the 80/20 rule, the law of the vital few, or the principle of factor sparsity) states that, for many events, roughly 80% of the effects come from 20% of the causes.
The principle has a wide variety of applications but the general meaning of the idea fits your context well, that a disproportionate (80%) of net effects come from just (20%) of the effort (causes).
It's an idea frequently used in management circles, where division of labor to achieve some specific result is studied quite closely, but also has wide application outside the world of management.
Words like exponential and high-yielding are often found used in situations referring to processes where the output is markedly high compared to the input.
His shrewd financial decisions resulted in exponential growth.
I would always advise you to invest your energy in high-yielding projects.
Other (controversial) words signifying colossal output relative to input (not that you should use them in your specific context) are atomic & nuclear!
A close match is an aleatory contract. I can define the exact meaning of the word with the following example: A life insurance policy is an aleatory agreement because the financial benefits can be greater than the premiums paid. Aleatory is something depending on a contingent event, but aleatory contract is used so often with life insurance that the usage of the term is closely associated with an agreement where "something that gives a reward or outcome disproportionately large to its effort".