The vacuous previsions really are rather trivial models. That seems appropriate for models of “complete ignorance” which is a rather trivial state of uncertainty. On the other hand, one cannot expect such models to be very useful in practical problems, notwithstanding their theoretical importance. If the vacuous previsions are used to model prior beliefs about a statistical parameter for instance, they give rise to vacuous posterior previsions… However, prior previsions that are close to vacuous and make nearly minimal claims about prior beliefs can lead to reasonable posterior previsions. (Walley 1991: 93)