Why did the sensitive plant (Mimosa pudica) evolve its leaf-closing mechanism?

There are many reasons why Mimosa pudica (More commonly now referred to as the TickleMe Plant) may have evolved it's leave- closing mechanism. I have observed the movement when insects have landed on my plants. The insects apprear to be frightened by the movement as they do move on rather quickly when the plant collapses. The movement of the TickleMe Plant also occurs when the sun sets or if I place the plant in a dark room. This may be a way to reduce water loss by transpiration as the leaves fold down upon each other. Another reason for the leave movement may be to expose the few thorns found on adult plants. This could be another warning for herbivores to stay away. In cold weather TickleMe Plants will close their leaves as well, could this be a way to maintain its body temperature. All in all, this is the most amazing house plant and I am always learning new things about this plant and its beautiful cotton candy like TickleMe Plant pink flowers.