Finding Ninja when building with build.cmake

In the Compile-on-the-command-line wiki page under the heading "Passing options to CMake" it shows how to specify building with Ninja by editing build_overrides.cmake.
It's unclear whether this is simply just an example of changing CONFIGURE_ARGS, or if it is a recommended edit.

But if I do include it, the build fails with
CMake Error: CMake was unable to find a build program corresponding to "Ninja". CMAKE_MAKE_PROGRAM is not set. You probably need to select a different build tool.

How do you define CMAKE_MAKE_PROGRAM? And what does choosing Ninja achieve? Just a build speedup?

Thanks.