Are you growing in soil, and your you root bound?
I have not seen that grow, but I myself would never trim my roots, because at best it will stunt your growth, and IMHO, it could very easily kill your plants. I am a hydro grower but i do not touch my roots, the roots are the most delicate part of any plant and any damage to even the root hairs that come off the roots, and you could leave your plants unable to feed.
I have heard some soil growers that put slits in their roots when they become root bound to start the growth again because being root bound had them stunted, but I don't think that it is a good idea to even touch healthy roots.
If you want a way to maximize your plants potential give it some carboload or another source of carbohydrate, you will see a noticible difference supplementing carbohydrates as your plants will use its stores fast especially during flowering.
Sorry i couldn't be of more help, hopefully one of the other guys or gals will know more about this.