The higher-end Metz flashes can be set so the zoom reflector automatically provides a wider beam than strictly required to cover the field of view of the current lens focal length. This provides a more diffuse light with more reflections bounced from out-of-frame — nice, when you don't need all the focused power anyway.
Metz calls this "Extended Zoom Mode", and it's similar to the "even" illumination pattern found on some Nikon flashes.
The Metz 52 AF-1 also has a "Spot Zoom Mode" which focuses the flash beam more tightly, providing brighter light in the center of the frame with shadows in the corners. (Similar to Nikon's "center-weighted" illumination pattern.)
Of course, you can do this manually on the 36 AF-5, or on any flash in manual-zoom mode, but then you must remember to keep up as focal length changes. And note that the Metz 44 AF-1 and the ST version of the Sigma flashes lack a manual zoom mode entirely.