I believe you're asking a bigger question than you realize. Waste comes in all forms, but the biggest form of waste, in my opinion, is time. Sure, there is a considerable amount of material cost involved in when you have to do things over, but material costs vary and can be recouped relatively easily in other areas when you're mindful enough to observe.
Time costs are constant, and that's where you need to drill down to find waste.
In some cases, leftover "scraps" of material are better off in the dumpster due to the amount of wasted time dealing with them, and the storage space they require. Most often, the time you spend looking for the "perfect" piece of scrap to do a job costs more than new material.