The greenness of plants is very important for the process of "Photosynthesis" which converts the sunlight energy to food energy.
Greenness is a pleasant colour to the eyes which improves the eye vision.
More greenness is needed to make the globe cool from global warming, where green chlorophyll absorbs the heat and transpires the moisture to condense the clouds to rain.
Leaves greenness is the primary source of cosmic energy which gives life to the animal's body cells. (Animals are the secondary source of cosmic energy)
Greenness typically symbolizes life, fertility, renewal, and resurrection. Green is a mix of yellow (Varaahi) (which symbolizes glory and energy) and blue (Bala - Krishnam) (which relates to God and the heavens)
~ Dr. M S R Raju