Some people copy the walls from one layer to the other to create an existing plan and a demolition plan. This technique is not recommended. If you change the plan for any reason, you have edit the walls on two plans. If you use classes, you only have to edit the walls once. As well as that, you can use class overrides in viewports to change the graphics on the walls. You can't do that with layers.
We will be covering this topic in March 2016, book now!