adding namespace in IDL

adding namespace in IDL

I'm trying to add namespace in ATL server project via MIDL. To nest
classes definition generated by wizard in namespace I used MIDL feature
cpp_quote("some string") that MIDL injects into generated files. To build
project I did following:
added cpp_quote("namespace ns {") before first interface declaration in
the IDL file;
added cpp_quote("}") at the end of the idl file;
nested generated by wizard coclasses in the same ns namespace.
added ns:: to LIBID_* name in generated dllmain.h.
What are cons of this approach ?