Splitting a larger OSPF area into a number of smaller areas has several advantages for network scalability and performance. Some of these advantages are:
It increases stability by limiting the impact of topology changes within an area. When a link or router fails in an area, only routers within that area need to run the SPF algorithm and update their routing tables. Routers in other areas are not affected by the change and do not need to recalculate their routes.
It reduces processing overhead by reducing the size and frequency of link-state advertisements (LSAs). LSAs are packets that contain information about the network topology and are flooded within an area. By dividing a network into smaller areas, each area has fewer LSAs to generate, store, and process, which saves CPU and memory resources on routers.
It reduces bandwidth consumption by reducing the amount of routing information exchanged between areas. Routers that connect different areas, called area border routers (ABRs), summarize the routing information from one area into a single LSA and advertise it to another area. This reduces the number of LSAs that need to be transmitted across area boundaries and saves network bandwidth.