Statically linking to libstdc++ is a tip to use the library embedding in the application regardless with the version of libstdc++ on target.

Optional, and harmless

(unless you’re using a system library written in C++; very rare indeed on unix).

And, sometimes is necessary if producing binaries to run on systems with different versions of libstdc++ (or none). 

The following figure shows how to use the static linking with Tizen SDK.