This object reports the sequence number of a specific link-state advertisement in the database, a monotonically-increasing value OSPF uses to determine which of two copies of the same LSA is more recent, with larger meaning newer per the description. It matters when an admin is manually comparing LSA copies between two routers that seem to disagree about a piece of topology; the router with the higher sequence number for that LSA has the authoritative, more recent version. Seeing one router report a noticeably lower sequence number for the same LSA than its neighbors would flag that router as running on stale topology information, likely due to a flooding or adjacency problem.