Pagerank centrality measures the probability of arriving  at specific node by traversing edges. Thus the higher the value of a node, the more "important" it is. Essentially this becomes a measure of centrality derived from a nodes neighbors, proportional to their out-degree.This is again used to measure bottlenecking, but also used as a comparative metric so that various networks could be compared in terms of their structure, both visually, and quantitatively.