Mature coconuts fall off naturally, but they taste yucky. All the water dries up & becomes milky. If you don't harvest young coconuts during the prescribed interval, the water becomes undrinkable. But we use mature coconuts for oil. You crush it & set it out to dry in the hot sun, make coconut flakes etc. Also, its dangerous to let coconuts stay up like that. In every village there's always 1-2 stories of kid who died when playing in the orchard because dried coconut dropped on him.