Using GetTag without searching through fallbacks makes it possible to detect which subshader is currently being used: add a custom tag to each subshader with different value, and query the value at run time. For example, Unity Pro's water uses this function to detect when the shader falls back to non-reflective one, and turns off reflection camera in that case.
Можно проверять скриптом какая из версия шейдера (какой Subshader\Fallback) используется.
