It all depends.
Some will say that if you top, you will just be dividing what would have grown in one cola, into 2 or more colas. In my experiences topping did not help weight that much.
I use it more for if I have a tall girl that I can't put into flower just yet. I top her to keep her low.
I only fim normally by accident, which is how fimming started, (FUCK I MISSED) It's when you go to top and you miss and 3,4 or more colas pop up. You get similar results as topping, just more colas.... more bushy....