When is it necessary to use the flag -stdlib=libstdc++?

When is it necessary to use use the flag -stdlib=libstdc++ for the compiler and linker when compiling with gcc?

Does the compiler automatically use libstdc++?

I am using gcc4.8.2 on Ubuntu 13.10 and I would like to use the c++11 standard. I already pass -std=c++11 to the compiler.