Toggle Visibility of Pieces

There are times when you don't want to see everything. For example, you're working a pit, but it's hard to see what you're doing because the room above keeps blocking your view. You can toggle the visibility of things in the Render Window by pressing the '1' key. First press makes it transparent, second press makes it invisible, third press bring it back to full visibility. Of course once something is invisible you can't click on it anymore, so you can press alt-1 to make all objects visible again in the editor.

You can change this and many other settings in the Render Window Hotkeys window, under the Edit pull-down menu.