The wastage aspect is one part of being environmentally friendly...

The wastage aspect is one part of being environmentally friendly but also you have to look at the processing and energy to manufacture the materials. The manufacture of concrete blocks is very energy intensive.

For example to produce a wall 5m long and 2.5m high and 110mm wide uses 3.3t of concrete blocks let's say 3t to allow for the holes in the block. The embodied energy of that wall is 3000kg X 1.5MJ/kg = 4500MJ.

To build using timber and plaster uses 45m of pine (say 90x45) which is 180kg. And 25m2 of plaster which is 142kg. The embodied energy of that wall is 180kg x 3.4MJ/kg plus 142 x 4.4MJ/kg = 612+624= 1238MJ.

Building a concrete block wall uses 3.6 times the energy than a stick build. As far as being environmental, concrete blocks are terrible for internal walls. They are however better than clay brick for external walls but worse than weatherboards. Wastage is an environmental side issue compared to manufacturing energy.

http://www.yourhome.gov.au/materials/embodied-energy