A hand-made watch has parts fitted to each other. A factory watch has parts made to a tolerance, so any correct part fits any movement of that model and run. That single difference reorganises the whole trade.
American factories designed movements around machine operations from the outset, standardising plate layouts, screw threads, jewel settings and staff dimensions. Production was recorded in runs, which is why factory serial evidence is comparatively rich.
Repair changed with it. Where a nineteenth-century English watch needed a part made, a factory watch needed the right material ordered by grade and size, and material catalogues became essential bench references.
The consumer effect was reach rather than luxury. A reliable jewelled watch moved within the means of railway workers, tradesmen and clerks, and the pocket watch became an ordinary possession rather than a status object.
For researchers the archival consequence matters most: factory production implies records, and records mean an ordinary movement can often be dated and specified more precisely than a fine hand-made one.