I ran an experiment with two clones, same age, same treament, substrate, etc. One was topped, the other left to grow natural, and both gave out exactly the same weight to within a gram.
However, I do believe from others experiences that I have talked to, that like most things it is strain specific. Some plants are happy being topped, produce more vigourous growth, and do not loose anything as far as the flowers weight being distributed across colas. Others simply don't benefit.
It also depends on your growing style, you could say topping could be likened to supercropping, which ultimately on the right strain can produce fatter harvests.
If I want multiple tops I just tend to put a stake in the pot and tie the top down below the last node and eh voila, multiple tops created, or the further you bend down, the more tops you get....
I think it's a great topic of discussion though.
Peace, DST