In the essence, the node allows you separate node networks in material editor, depending on if it is being compiled for present or previous frame.
You would plug that into world position offset, and use your typical WPO animation for Current frame, while adding some compensatory value to the this animation for Previous frame. To get rid of temporal blurring, you might want WPO for previous frame to appear the same, as for Current frame. Thus if you are using something simple for WPO, like sin(Time)*VertexNormal, for previous frame it should be sin(Time+FrameTime)*VertexNormal, where frame time should be supplied as parameter from blueprints/code.