Balancing an engine

This is not a case of whether or not I am going to get my rotating assembly balanced. I have a stock 340 forged crank, aftermarket forged pistons and forged H-beam rods are coming. This is a high HP application and I will be getting it balanced. I have just never heard of when you should and when you don't have to, and was curious. Obviously with the responses in this thread it was a good question. hehe

Jack