theres really no such thing as a leaf sucking energy even the ones in the shade still produce enough energy to prevent them from sucking energy from the rest of the plant. photosynthesis happens much more efficiently when there is less light, there could be 100 times less light but the leaf my produce only 10 times less energy ( just an example not actual numbers) the purpose of leaves is to generate glucose for other parts of the plants once a leaf is matured and no longer getting larger it has very little energy needs for itself. how ever leaves do age and there efficiency can decrease over time, they can block out light from other more efficient leaves and buds and restrict air movement and transpiration which can ultimately restrict photosynthesis . large fan leaves can also slow the growth of lower branches. in veg it really doesn't matter as long as your canopy is full when you start flowering excessive defoliation will slow growth in veg. In flowering i personally do not remove any unless leaves airflow is restricted or maybe if they are blocking out light from buds but for me it is preferable to just tuck them out of the way . even when i lollypop i only remove lower buds not healthy leaves . the lower leaves aren't in the way of any buds and as i said i do not believe they will suck energy from the plant. in flowering energy is focused on flowers. if a leaf is not getting enough light to sustain itself it is more like to just slowly die as opposed to sucking energy.
