In this new post to his blog Stoimen Popov talks about calling the "destructor" method of an object and why doing it directly could lead to some issues - like not actually destroying the object before the script ends.

At the end of the script the interpreter frees the memory. Actually every object has a built-in destructor, just like it has built-in constructor. So even we don’t define it explicitly, the object has its destructor. Usually this destructor is executed at the end of the script, or whenever the object isn’t needed anymore. This can happen, for instance, at the end of a function body. Now if we call the destructor explicitly, which as I said I’ve seen many times, here’s what happen. As you can see calling the destructor explicitly doesn’t destroy the object. So the question is...how to destroy an object before the script stops?

He points out that one way to "destroy" an object is to null it out and remove the structure from memory. This is tricky, though, because a clone of the object will still exist in memory, just not the original.