Adjusting Layer Transparency
Adjusting the transarency of a layer can be very handy. For example, the topo contours layer will hide the aerial imagery or land ownership boundary layers from view. By adjusting the transparency of the contours you can visualize the layers underneath. And because the topo contour overlay images can be fairly large, it is sometimes faster in Goolge Earth to adjust contour transparency than it is to constantly hide/show the contours.
Example: Viewing Topo Contours On Top Of the Aerial Imagery