Wide angle is meant for small micron backs (P40/P65+, IQ140/160/180, Aptus II 8/10/12, Credo 40/60/80) when used with Schneider Wide angle lenses like the 35XL. It does additional correction for some kinds of artifacts unique to these combinations. When in doubt I use this option. When it's clear that it doesn't apply (i.e. 72XL with a 45+) I turn it off.
The option to exclude dust correction makes the LCC calculation much faster, but precludes the option to remove dust from the image based on the LCC. This option is appropriate to check if you follow the "library" method of LCC.
I find I often correct 100% of the fall off but then add slight vignette to reference/simulate/echo the natural vignette of lenses that dominates many classic landscapes. It focuses the eye inward in the frame and prevents the eye from "falling off" the edge. But by doing it with vignette after fully correcting the natural vignette I insure the amount of the vignette is the same from one image to the next regardless of aperture/lens/movements used and regardless of whether the full frame was used or only a crop (imagine a crop of the left side of the frame, the natural vignette would only be on the left side, which is just visually awkward).