If you want to understand why Southern Pine Company of Georgia has a purpose,watch this video http://www.thisoldhouse.com/toh/video/0,,20185345,00.html. By demoing,the building material of the previous home is lost to the landfill. The demolition occurred due to the trend of modular building not the reason of poor conditions or the materials not reusable.
A Random Demolition
When a deconstruction occurs,we are able to take the materials and separate them as they are removed. The wood can easily be transported to the workshop for denailing then either run through for alterations or kept in storage,not in the landfill. The same with any other materials reclaimed from the deconstruction.
What is a plus to modular building? It can be built out of reclaimed materials,the same materials used from a previous structure.