See a point of interest in a layer that appeals to you? You can copy any placemark that appears in a layer and paste it into My Places (right click > Save to My Places). This is useful if you want to display this placemark, but not the entire layer.
It also allows you to view the KML behind an attractively presented placemark or balloon (learn more). I do this as a way to reverse engineer how a placemark was built in KML or HTML, which can inspire KML I author in the future.