It’s also not “necessary” for regen braking depending on your car. Early EVs (and AFAIK) current Teslas do not blend regen braking with the regular brakes, so you needed to use one pedal driving to get the most range. Modern, well made EVs blend the regen braking with conventional brakes on the same pedal, so you don’t have to use one pedal driving mode to get the most range.