Most of the contractors i know, always say time is money, and i guess for them it is. if your bidding on a job ya want in want out quick as possible. And i'm sure liability could be an issue about letting somebody on the jobsite thats not on the contractor payroll.homeowners might not care for it. The time is money thing does lead to a lot of waste, the old school guys would use up the scrap stuff to try to save on material, lot of them just go grab another sheet to cut, quicker than dealing with the scrap stuff.