The reason for including this argument is that SLIC-zero normalizes the spatial distance by seed step, and color distance by maximum color distance within the cluster.

Also... I started wondering: the two normalized distances are combined by adding them together, but in principle they could be combined with unequal weights. It seems that it's really just a clever way of choosing a reasonable weight automatically and locally as opposed to being truly zero-parameter. But I could be wrong on this one...