This is quickly becoming one of my favorite tools. When I'm setting up my paperspace viewports, I used to use the layer drop down list to freeze the layers I didn't want displayed. This has always been a tedious process & I've often thought there should be a better way. Today I tried layiso to isolate the layers I wanted to see in my viewport. It worked like a dream. It only isolates layers in the active viewport & the rest of the drawing is unaffected. Perfect!