Curie's parameters for choosing gleaning victims suggests that she's trying to mimic the Age of Mortality in such a way as to give people a sudden end when they seem done living—which, the novel might suggest, doesn't necessarily happen when a mortal person reaches what would be considered old age. This may give some people freedom, though Curie's meditations on stagnation and boredom suggest that she doesn't see immortality as a great thing for these reasons.