Power Draw
You're probably here for this, as the only rationale for an i9-12900K to be restricted to E-cores is power savings.
Energy Efficiency
In this section, we measure the total amount of energy consumed for a SuperPi run (single-threaded) and Cinebench (multi-threaded). Since a faster processor will complete a given workload quicker, the total amount of energy used might end up less than on a low-powered processor, which might draw less power, but will take longer to finish the test.