[10 [b c]] is a "function" that throws away b and just applies c to the subject.
However, if b is a cell, its second component is applied to the subject first (before also being thrown away).
This reduction makes this a little clearer:
*[a [10 [[b c] d]]] =>
*[a [8 [c [7 [[0 3] d]]]]] =>
*[[*[a c] a] [7 [[0 3] d]]] =>
*[*[[*[a c] a] [0 3]] d] =>
*[a d]
although I'm still a little confused how this would be used in practice.