A modeling light mode causes the flash to strobe for a brief time, temporarily providing the effect of a constant light. This allows one to directly see where shadows will fall before taking a photograph. This is more important with film where there's no other easy way to get instant feedback, but can still be useful in the digital era. The entry-level models from each manufacturer are missing this feature, but most middle and higher-end models all have it.
The Metz 44 AF-1 has the capability to fire a 3-second modeling light, but there is no control for it — it instead depends on a corresponding control on the camera. Since no Pentax camera has such a control, the modeling light is not actually available to us. More advanced Metz models have direct buttons for triggering the modeling light.