BOTH! I top and tie them in veg. When I move into flowering room I cut the ties and weave the branches through the screen. Then as they grow even more I tie a few of the branches to the screen to keep them from shading each other.
One thing for sure.... don't put plants you aren't SURE are female into the screen. It's harder to cut out the males once they are woven into the screen....and if you are pulling and shaking them while trying to cut them out you could release pollen.