I ma believer of pruning, when necessary. My theory is that the energy that the plant uses to feed and keep they leaves alive can be used for new production.
Think of it this way, there are as many roots as there are leaves, by removing sick leaves, you will now have more roots per leaf. WIN!
I could be horribly mistaken but that's what goes through my mind. Hey, it seemed to work for you.
I've always wondered whether lower branch leaves are a drain or a benefit to the plants nutrient economy. Obviously they take "energy" and nutrients from the plant to build and maintain, but the whole point of leaves is photosynthesis.