Prior to C++11, you would usually define static_assert as a macro (a typedef that would be invalid if the condition is false), so it can be available from anywhere (namespace level, or function level) and still not be ambiguous (e.g. by using a line number).
The Boost.Preprocessor library is another good example of using macros to reduce the amount of highly redundant code, and another one that is less relevant with variadic templates.
Furthermore macros are widely used to "talk" to the compiler, e.g. checking what compiler you are running on, what version of the compiler, whether C++11 support is available, etc.
