In some cases where the model form is dependant on vertice position, Simple vertice deletion will not just delete the vertices without a little bit of model recalculation. From what i understand the delete key just attempts to remove said vertices from object, while the Delete vertice function removes and reconstructs a little of the history of the object to achieve a new shape.
.....Just an educated guess though so, ...?
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And after calming me down with some orange slices and some fetal spooning,
E.T. revealed to me his singular purpose.
--TOOL, 10,000 Days---
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