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It created jobs, and One effect was the division/specialization of labor. So whereas once one person would create a product from start to finish, mass production resulted in many workers each building one part of a product.
It made them much larger. In mass production the efficient transportation of what you're manufacturing or assembling from one stage to the next becomes very important. Hence you want the stages as close as possible to each other. That calls for a very large factory floor. It also prioritizes the location of factories near means of heavy transport, like canals, rivers, lakes and railroads, because again you have much bigger transportation issues when you are manufacturing things in one place and selling them somewhere else. (In an artisanal economy, you often manufacture and sell in the very same place, the artisan's workship is also his salesplace.) So that would place a premium on concentrating factories where heavy transportation is easy -- accounting for the massive growth of railroad nexi like Chicago, or important river junctions like Pittsburgh.