This read-only Counter64 is the count of bytes sent over this specific underlying Path. An admin uses this to see how traffic load is actually distributed across the multiple physical paths that make up a single VPath, verifying load balancing is functioning between, say, an MPLS-based path and a broadband-based path. For example, if one path within a VPath carries the vast majority of bytes sent while a sibling path carries almost none, the admin may investigate why load isn't being balanced as configured.