DRAG, DROP AND DRILL
In a dual-pane Explorer view, if you're dragging a file or folder from the right pane to a buried folder in the left pane, you don't need to expand the folders first. Select the files or folders you want to copy, drag them to the left pane, and hold them over the contracted folder for a second or two. The folder will expand automatically, so you can drop the files into the folder or continue drilling down.