What is the purpose of libstdc++-dbg?

The Synaptics package manager says that:

This package contains the shared library of libstdc++ compiled with debugging symbols.

But I can successfully print the contents of std members in the debugger without having this library. This is probably because most of them are templated, so the compiler can see the entire source code. But what good is a compiled library where the user cannot see the source code?

I am really confused. Please, could you explain?