Once scene objects are driven by the Time Editor, you may need to temporarily disable the Time Editor to make adjustments to your animation. The Mute/Unmute the Time Editor option lets you switch back to Maya's non-Time-Editor driven mode (also known as Scene Authoring mode,) by temporarily disconnecting all attributes to author new animation (including constraints, expressions, Driven Keys, and so on). This way you can add new animation to your scene that you can add to the Time Editor.
Mute/Unmute the Time Editor lets you add animation instantly to a scene, without importing animation.
See Animate attributes with the Time Editor for an example of a workflow where a scene is edited outside of the Time Editor using Mute/Unmute the Time Editor.