Imagenette/woof: what's the 160px size for?

In the Imagenette/woof code, there are 3 pixel size options: px: 128,192,256.

Looking at the dataloaders, there is the code:

def get_dls(size, woof, bs, sh=0., workers=None):
  if size<=224: path = URLs.IMAGEWOOF_320 if woof else URLs.IMAGENETTE_320
  else        : path = URLs.IMAGEWOOF     if woof else URLs.IMAGENETTE

Why is the IMAGENETTE_160 never used? What is it for?

Also, in general, could someone say what the different pixel sizes are really for? For example, why do we want to resize to 128 from something with a 320px minimum dimension?

Help is appreciated!