To grow some high quality marijuana, the plant needs to make a lot of sugars first. It's very important that these sugars go to the right place, because buds and young leaves use these sugars to grow. The full grown leaves produce these sugars so they are also very important. But how are sugars produced and can you increase the production by trimming away leaves? In general I advise to keep leaves in place till the plant discards them of by itself. I'm talking of course about the large fan leaves. Trimming young leaves and young side shoots can however lead to better distribution of sugars (=higher yield), but only if your plant retains its larger fully grown fan leaves. A plant catches sun rays on its leaves and converts this energy along with CO2 and water into sugars. This process is called photosynthesis. The evaporation gives the plant the chance to take up water and nutrients through its root system and transport them throughout the plant. Sugars in particular are very important building blocks for the plant. The sugars are carefully divided to specific parts of the plant. The actual yield depends mostly on the amount of sugars the large fan leaves can produce and the amount of sugars that are eventually transported to the buds. You can roughly say that two thirds of the sugars go to the buds, which is a lot. Young foliage that's still developing also requires these sugars. Noticeable is that every plant has a fixed ratio when it comes to dividing the sugars. These ratios, sadly, are hardly influenced by nutrients, temperature, light or CO2. We are only interested in the buds, so it would be nice to be able to influence the distribution a little bit. Distribution of sugars through sink strength The principal behind the distribution of sugars is the so called sink strength. All the plants organs function like individual sinks which the sugars flow towards. However the suction of the sinks are not equal in strength. The buds have the most suction, especially when they are half way in their development. Young, new foliage also needs a lot of sugars while matured leaves create more sugars than it needs. These old mature leaves provide the buds and young foliage with sugars and for that reason they are very important. Within the plant there is a lot of competition for the sugars. All parts of the plant are pulling on the available sugars. Pulling harder means more sugars. So organs with larger sink strength always get more than the ones with lower sink strength. Example: a main bud with sink strength of 3 will get 3 times as much sugar than a leaf with sink strength of 1. These ratio's always stay the same, whether there are a lot of sugars or hardly any available. Trimming plants for a better distribution With the above mentioned principals in mind we can now start to trim the plant for a better distribution of the sugars. By removing young foliage before they start to use up energy, more sugars will automatically go to the buds. Pay close attention when removing. Make sure the plant keeps enough foliage and fan leaves to make sugars. The foliage needs to be dense enough so no light can pass through to the pots, so we don't waist energy. Personally I would not trim fan leaves. The top fan leaves catch the most light and automatically have more chloroplasts, so they can produce more sugars. But the bottom foliage also catches a little light and contributes to the sugar production. Why remove a fan leave when the sugar production is higher if you leave it be. In the event that a fan leave is that much overshadowed by the top leaves and it's actually using up more sugars than it is producing (becoming a sink, once again). The plant will then sacrifice suck dry and disregard this leave and it will fall off by itself. The plant has its own solution for such matters so why not just leave it to the plant.