[codr7]

From my experience, writing your own gives you a level of control and leverage not achievable through a third party VM that might be worth it once you get some practice. As long as you haven't tried, you have no idea about the trade-offs, goes for anything.

Same goes for not compiling all the way down to byte code (or even worse, C), makes some things easier to implement and allows more flexibility because of the lack of separation between compile time and run time.