An anytime algorithm monotonically improves some evaluation metric. For a sort, the evaluation metric is usually the number of inversions in the list. At completion, there will be zero inversions. If at time 0 there are N inversions, then at time 0 < t < completion time there will be ≤ N inversions; that is, the list is "more sorted" than it was before. As the various examples about games and animation elsewhere in the comments show, this can be interpreted as "somewhat smoothly moving towards sorted over time," which is an (occasionally) ((rarely)) useful property.