Optimization means getting the same result(or a better one) using fewer resources.
In mining, one of the most important things to optimize is energy efficiency.
Energy efficiency tells you how much power(electricity) you use to produce a certain amount of hashrate.
It is usually measured in W/TH(watts per terahash)
Example
Conclusion
Even if the second ASIC is more powerful, it is less efficient because it consumes more energy for each TH.
This means: The lower the W/TH value, the better the efficiency.
Newer or higher-quality devices usually have lower W/TH.
Keeping hardware cool improves performance and reduces energy waste.
Lowering voltage to reduce power consumption while keeping similar performance.
Choosing efficient software with low overhead and low dev fees.
Selecting pools with lower fees to keep more of your rewards.
Optimization is basically about this: maximize hashrate, minimize costs(especially electricity)
If you want to calculate efficiency, visit the Efficiency Calculator page.