There is a reported but unproven theory that water stressing (withholding water) the plant can add to trichome production late in flower. But that is far different from humidity. Humidity and temp are what causes the stomata of the plant to open and close. This is how the plant regulates its water levels and absorbs nutrients. With too high of humidity, they close up and the plant stops drinking. Too low of humidity and they remain open, pumping water from the roots to escaping the stomata back into the air. Sounds good, but you don't want to leave the gates wide open, the plant will work too hard and increase of nutrient burn and other ill effects typically follow.