I think it is about pleasing looking grain. IMO FP4+ in smoothie developers looks awful once the grain is visible, but wonderful at very small sizes. Delta 100 on the other hand retains crisp grain in Xtol and a 19 inch print on my wall from 35mm shows very small, right, sharp grain. Its remarkble really. However, in the main I am moving towards more acutance and sharper looking grain for precisely this reason. As an image becomes less 'sharp' as the enlargement grows, retaining sharp grain, even if the image gets more crude, retains a sense of precision and 'rightness' unless the scene is one where grain is objectionable. This is why I am using FX-39 where I can, Xtol when I dont want much grain etc. I have done a recent experiment on mixing the two to get crisp but not excessive grain off faster films and it worked....This was all on 120. In 35mm, using slow films, FX-39 gives a remarkable sense of sharpness and crisp grain up to large sizes. To me, solvent developers produce grain that just does not look pleasant when enlarged a lot, esp it the image suits a crisp look. For tonally smooth scenes enlarged to a lesser extent they make more sense IMO