From the official documentation here: Shutting down and disconnecting from the server

You can rely on garbage collection to destroy the OLEObject variable. Destroying the variable automatically disconnects from the server.

It is preferable to use garbage collection to destroy objects, but if you want to release the memory used by the variable immediately and you know that it is not being used by another part of the application, you can explicitly disconnect and destroy the OLEObject variable

So you can keep the destroy w/o the disconnect. As for the destroy itself, it depends on the type of object. You don't have to do it, especially for in-process objects. Usually, it's used for COM objects such as Microsoft Word or Excel (when you want to make sure the exe is really gone when you want it to be gone).