Hey Growmie,
Removing lower leaves and branches can make the plant focus its energy on the top part, where the bigger buds are being produced. By carefully trimming unnecessary branches and/or leaves we avoid wasting our plant’s energy, this energy can then be redirected to the development of the main buds, resulting in bigger and denser flowers. You should start pruning by removing a couple of leaves a day or for better results every 2 to 3 days, starting when your plant is 3 weeks old up until the pre-flowering stage.