The transmission can't tell the difference between flooring it on the freeway on-ramp vs. flooring it to pull rocks up a hill.Towing with a rope/chain is always a bad idea if not illegal, but the transmission is the part of your car that you'd be over-stressing the most.
Imo, it's not worth jeopardizing the health of your car for a friend that simply wants to save a few bucks.
Pulling a car won't damage the transmission unless you really try to flog it.

