Number of streaming Textures with mipmaps currently loading.
When adding a new camera it can take a few frames to detect which new Textures need to be loaded. Therefore this value can't be relied upon immediately. If any objects move or the camera moves then this value will change so it's not guaranteed to drop to zero.
When implementing camera cuts it is recommended you have a minimum time to allow mipmap levels to be calculated and maximum time to wait before doing the cut. This property can be used with a value between the min and max time in order to cut earlier if the mipmaps are loaded in time.
最短时间取决于场景中的渲染器数量和每帧处理的数量。帧最短延迟计算公式为：(Texture.streamingRendererCount + (QualitySettings.streamingMipmapsRenderersPerFrame-1)) / QualitySettings.streamingMipmapsRenderersPerFrame。 最长时间应该在用户可接受的延迟范围内。例如，0.5 秒（或者 30 帧/60Hz）。