I feel just the opposite if your are going to train a plant to either bush or grow up in a certain direction you need to trim. Marijuana is capable of training and withstanding pruning just like banzai tree's.
Just make sure that you don't trim more than one or two fan leaves for every foot of plant per week. The only time that this is going to affect the plant adversely is if you over trim or try to trim during flowering when the hormones have changed throughout the plant.