I'm in the camp that believes that topping a plant does not increase yield. What it does is redistribute that same yield from one location to several locations. I grow outside and top all my plants once. Some plants will be topped a second time if necessary. Any plant that has been topped will require a longer veg period. They need a few days to recover from the temporary stunting, and then you want to veg them longer to realize the gains from being topped. The reasons that I top my plants are: 1) To avoid excessively large main colas that are susceptible to mold. 2) To minimize larf, and 3) To control height, because not everyone can get away with 12 foot tall plants in their backyard. I think Welcome to the Grow Tent on YouTube has good videos explaining the how and when of topping plants.