The Weight of each animation layer determines how much of its animation plays in the result animation in your scene.
Keyframing the Weight value of animation layers lets you blend the effect of the layer in and out, animating how much the layer influences the result animation in your scene at any given time.
You can set the weight of animation layers using the weight keying buttons (
 and 
		
) or the 
		Weight controls in the 
		Animation Layer Editor, or by selecting the Layer node and editing the value in the 
		Channel Box. 
	 
To keyframe the weight of animation layers
You can also quickly set and key the layer 
				Weight value to 1 
				
 or 0 using the 
				
 
				Animation Layer Editor buttons. 
			 
You can use the Time Slider, Graph Editor or Dope Sheet to view and edit the keyframes you set on the Weight value of animation layers. See View layer weight animation.