Clarify optimization instructions

(cherry picked from commit 2ed5a658222741199f59c18ed166abc77886cace)

tutorials/optimization/gpu_optimization.rst

@@ -88,9 +88,11 @@ possible. Godot's priorities are:
    scene, the faster the rendering will be. If a scene has a huge amount
    of objects (in the hundreds or thousands), try reusing the materials.
    In the worst case, use atlases to decrease the amount of texture changes.
--  **Reusing Shaders:** If materials can't be reused, at least try to
-   re-use shaders (or SpatialMaterials with different parameters but the same
-   configuration).
+-  **Reusing Shaders:** If materials can't be reused, at least try to re-use
+   shaders. Note: shaders are automatically reused between
+   SpatialMaterials that share the same configuration (features
+   that are enabled or disabled with a check box) even if they have different
+   parameters.
 
 If a scene has, for example, ``20,000`` objects with ``20,000`` different
 materials each, rendering will be slow. If the same scene has ``20,000``