If a vbox has more room than needed for its children, the policy can be defined with VBox.vgrow. The other way around cannot be adjusted though: if there is not enough room and the vbox starts shrinking its children there is no way to give preference to particular child nodes.

This becomes apparent in the code example on the first comment. Here a label is supposed to wrap over two lines but that does not work because it competes with a big listview for whatever space is left. A more plausible result would keep the label wrapped at the expense of 17px less for the listview.

I suppose the same case can be made for hbox, and possibly other layout panes.