The Tips in detail

 "If you start building complicated scenes (like "My Room" or "Sat Dish"), you should learn to use basic geometries as positional dummies."

This makes it a whole lot easier to build your scene while specific objects are not ready or even don't exist at all and saves RAM and CPU-power during test-renderings which means a dramatic increase in speed.

Give them a simple dummy-material like grey plastic without any submaps. This way you can check out the distribution of the objects in your scene more easily.