There is a lot we do in chi-sao we dont do in actual fighting. We adopt a mutual facing starting point from which to move off the center of a clock face, relative to lines of force and movement , angling, etc......We adopt roles for each other so we can help develop ideas of attacking and countering attacks.
In chi-sao the fight should be with your elbows and hips not to collapse backwards, not a fight to beat up the guy helping your elbows and hips achieve their goal
Does a boxer beat up the guy holding the pads for his combinations ? no
Does a boxer knock out the guy coaching him with footwork ? no
Do you bite a heavy bag in a clinch with it
no why ? because you're training with partners , pieces of equipment enhancing your ability to fight...a sparring partner is not a guy you're out to ko with bombs....you're working ideas, hes throwing stuff for your benefit to react to and counter....seeing a dropped hand as you deliver a strike, a telegraphic shoulder...an off balance counter.
So WHY in chi-sao does everyone try to beat the guy they are training with ?