FALSE!! If your plant is already flowering you would be best served by LEAVING IT THE FUCK ALONE until its done and you have a great harvest.
How well do you cope when someone comes and takes all your food away? those big leaves are what makes and stores all the food your plant needs, cutting them off is not recommended. If the plant does not need a leaf it will suck all the life out of it and the leaf will turn brown and shrivel and fall off on its own. no help is needed from us to do this.
Your friend has grown how much weed?