Some (well, most) dynamic programming languages allow for an experienced developer to have an insight look into how their code is actually executed by the runtime environment.
They are able to see the parse tree and the compiled byte code.
They are able to see what parts of code are JIT-compiled, and how exactly the are compiled. When something is not compiled, they are able to see why.
The developer doesn't have to guess whether a particular optimization has kicked in or not. They know for sure how each and every object in their code is handled (whether it is CoW, passed by reference, passed by value).
I'd love to see these capabilities in MATLAB, too.