Presets and J/TH: how efficiency actually raises margin
Undervolting cuts watts faster than hashrate, so the power bill drops more than output - that is the margin.
The efficiency preset lowers chip voltage: on an S21 Pro, power drops about 16% while hashrate drops only about 4%.
Energy per terahash (J/TH) falls from 15.0 to 13.1. At $0.095/kWh that lifts daily margin by more than 15%.
The maximum preset does the opposite - more hashrate for peak-price hours. Rollback to stock is always one click away, so testing costs nothing.
One preset serves one goal. Max Output raises hashrate at higher power draw, Efficiency lowers J/TH so power drops while hashrate may ease, and Power Target holds the wall-power level you set. Advertised gains describe different modes, never one simultaneous result, and the exact effect depends on silicon quality, cooling and ambient temperature.