I think variable timing on a Lycoming would be great because when the mixture is leaned to ROP through LOP it moves the position of the peak pressure pulse towards top dead centre. This puts more stress on the engine as the power pulse occurs when the conrods are virtually straight up and down, resulting in "punching" the piston assembly into the crank. If the ignition timing can be advanced it'd move this peak pressure pulse futher away from TDC resulting in more efficient running and less stress on the engine bits, with the leanest possible mixture setting. It is easier for a computer to accomplish this, along with prop setting that fiddling constantly with the mixture and prop.