During college in the 1970s, I spent my summers working as a framer in residential construction; I was what was affectionately known in the trades as a nail bender. We would arrive at a building site a day or two after the concrete forms had been stripped off and stay until the roof was sheeted and the sheetrock and plumbing backers installed. Upon our arrival, there was a large lumber pack strategically placed by the delivery truck driver in a place only convenient for him. We would set up our saw horses, string our power cords, and begin cutting the floor beams, posts, and joists to length. If we cut something too short, we would send the greenest member of our crew to the truck in a futile search for "the board stretcher" but we were generally fairly accurate with our cuts and efficient with our lumber usage.
One developer we worked for decided it should be more efficient to pre-cut all of the headers, cripples, window plates, and window jacks in the warehouse and ship us a pack of pre-cut lumber. In theory, it would reduce labor, time, and waste at the building site. In practice, it often created over or undersized openings, sorting time that was sometimes more time-consuming than the cutting time it was supposed to save, and a need to call for more lumber to replace undersized pieces that could not be used, and became waste.
Prefabrication of building components has come a long way since then. The current focus is on commercial applications. Commercial building projects are often driven by schedule as much as cost. Using prefabrication methods can cut 30% out of a commercial construction schedule. It also can allow for fewer skilled workers on a jobsite, which can be beneficial in a labor-constrained market. The use of prefabricated wall panels can reduce the number of carpenters on site to fewer than 10. A cross-laminated timber installation crew can include as few as four. Another benefit, according to Dan Drinkward of Hoffman Construction, is that prefabrication of certain building components cuts down construction waste.
So, labor, time, and waste continue to be construction site drivers, just like they were "back in the day," but now prefabrication appears to truly be a viable solution in many applications.