Some homeowners like to install a subfloor over the main floor, with acoustic underlay between these two floor layers.
Acoustic underlay has several advantages. As the name implies it will dampen noise inside a room. The sound of people walking on the floor is greatly reduced. It will also greatly reduce any sound traveling to adjacent rooms, especially rooms below the floor. Acoustic underlay is ideal for apartments and strata as people downstairs will not be disturbed by the people in the rooms upstairs. Acoustic underlay absorbs most vibration and noise.
Acoustic underlay also provides a soft walking experience. This is not the same as carpets or rugs, but it is much softer than conventional wooden flooring. This reduces the impact when walking. If you find you get sore feet or sore leg joints from constant walking on concrete, tiles or hardwood floors then acoustic underlay will help alleviate the problem.
An advantageous side effect of acoustic insulation is that it also works as thermal insulation. Some people install thermal underlay for insulation to help keep temperatures stable in a room. Acoustic underlay will also provide quite good thermal insulation. This means the room stays warm when you use heating, and the room stays cool when you use air conditioning, all with less energy and effort. These is far less heat transfer to the outside environment.
Underlay of all types, including acoustic underlay, greatly reduces dust from getting into the room.
Floor sanding will restore a hardwood floor to its original new appearance.