If you ever watch a house being built, there's a huge pile of waste lumber from cut off ends. Carpenters don't look through the pile looking for an end to reuse, they just pull a fresh board and cut off what they need. With some careful design, and pre-cut pieces, one can nearly eliminate this wastage and cut costs substantially. It's not just the boards, it's the millwork, plumbing, carpet, etc.
When I was in construction all ends longer than a foot (30cm) were saved and most were used. They look like the are to be discarded, because most are created the first day and just sit there. However the very last thing before we leave we look around and verify that there is backing in all the corners to attach the drywall to. This used most of the longer scraps.
I recall reading about a spec house builder who would design the houses so that the dimensions of the rooms would fit an even multiple of the widths of carpet rolls. This nearly eliminated carpet waste, and made installation cheaper, too, as there were no seams.
