I don't currently have any " load vs drag " numbers to present , however, Back in the day- it made a difference.

if we look at amp draw numbers for fan, water pump and lights , lets say its 55 amps- put an alternator on an electric motor and look at the drag on the motor with a 55 amp load- its significant.
how much drag with modern alternators - im not sure.
I would think we could find the data somewhere.

When we go back to chassis Dyno , I plan to test load vs torque/hp at rpm scales.
My "guess" is it effects us most at shift points which means it effects driveshaft speed recovery.

might not be enough with todays alternators to fool with, then again, might be a slight consistency improvement in always running "no load " vs varied charge loads.

just the thoughts of an old bald headed guy.