В моно интепретатор появился для платформ в которых невозможен JIT (нужен либо полный AOT либо интерпретация)
http://www.mono-project.com/news/201...o-interpreter/
The main downside of full static compilation is that a completely new executable has to be recreated every time that you update your code. This is a slow process and one that was not suitable for interactive development that is practiced by some.
For example, some game developers like to adjust and tweak their game code, without having to trigger a full recompilation. The static compilation makes this scenario impractical, so they resort to embedding a scripting language into their game code to quickly iterate and tune their projects.