Tipster Richard Farlow reminds us that we can use AutoCAD layer states to manage the visibility settings in a viewport.
"Layer states work within viewports. After freezing layers in an active paper space viewport, it can be frustrating to turn a layer for a specific object back on if you’re not sure which one it is. My answer is to create a layer state in the layer state manager when I am in model space so I know all layers are on. I call it AO for 'all on.' When I’m working in a viewport, I can restore the AO state in the viewport and see all the objects within the viewport."
Notes from Cadalyst tip reviewer Brian Benton: Layer states can make your life easier, especially when setting up drawings and viewports, or even when revising old drawings. The layer state saves the conditions of your layer settings in order to reset them later. You can also do this with saved named views, which means you can zoom to a specific place in a file and turn appropriate layers on or off to see what you want to see.