Clock fit ups allow a clockmaker to build attractive, quality timepieces without the time and also bother of going back to square one with specific components. Clock fit ups (clock inserts) are preassembled systems that a person locations in a hole drilled with the case. This strategy is especially appealing when the emphasis of the endeavor is on developing as well as creating the framework rather than on putting together parts.
Clock fit ups do have some downsides that can limit their appeal. All components (hands, dials, lenses, bezels) are preselected, constricting layout options. If you do not like any one of the readily available mixes, you're out of luck.
But also for some clockmakers sufficient is obtained to make up for needing to sacrifice liberty of option. Saving time, as already mentioned, can be a big gain. An additional is when a musician wants to convert a fancy masterpiece right into a wrist watch.