Clock fit ups allow a clockmaker to develop attractive, quality timepieces without the moment and trouble of going back to square one with individual components. Clock fit ups (clock inserts) are preassembled units that areas in an opening drilled via the case. This approach is specifically appealing when the focus of the endeavor is on creating as well as building the structure rather than on setting up components.
Clock fit ups do have some downsides that can limit their appeal. All elements (hands, dials, lenses, bezels) are preselected, constraining style alternatives. If you do not like any of the offered combinations, you run out luck.
But also for some clockmakers sufficient is acquired to compensate for needing to compromise flexibility of option. Saving time, as already discussed, can be a big gain. Another is when an artist desires to transform a fancy showpiece right into a wrist watch.