Many lizards have impressive tail [see the photo on the right]. And equally eye catching is their ability to drop the tail, or part of it, which may be regenerated later [rollover for an example]. The common understanding of the feature is that this is a defense mechanism, called autotomy, to elude a predator's grasp or to distract the predator and thereby allow escape. I doubt this is the only function of the self amputation - evolution is known to effectively "solve" numerous life problems simultaneously. It’s remarkable, for instance, some lizards will return to a dropped tail after the threat has passed, and will eat it - implying that the tail could be a major storage organ for accumulating reserves.