Key Opacity

This is useful when you have a layer that hasn't got any keyframes in its Opacity channel, but you want to animate the opacity starting at some point in the timeline away from frame 0. There are other ways (e.g. force the opacity channel to be visible; open up the layer settings and make a manual change to the opacity to create the key, then set it back to the frame 0 value), but these take more clicks to get there. 

This is a one-click [color=#000000][size=3][font=Roboto, sans-serif]to enable animated layer effects and [/font][/size][/color]to set the layer opacity to the frame 0 value at the current frame.