If you top your plant during the flowering stage you will take off the very nodes that your plant needs to grow the bud. During flowering the plant is concentrating on budding and then croaking. It will NOT grow any new branches during this time. That's why it is important not to top your plant unless you leave enough veg time for the plant to regrow. All you would be doing at that point is cutting down the plant and the very growth it needs to flower with. Topping must be done during the vegging period.