すべてのシェーダーに適用されるグローバルな Float プロパティーを設定します
Global properties are used if a shader needs them but the material does
not have them defined (for example, if the shader does not expose them
in Properties block).
Usually this is used if you have a set of custom shaders that all use
the same "global" float (for example, density of some custom fog type).
Then you can set the global property from script and don't have to setup
the same float in all materials.
関連項目: SetGlobalColor、SetGlobalTexture; Material class、ShaderLab ドキュメント.