Hello zaman
According to Cisco:
The OSPF Graceful Shutdown feature provides the ability to temporarily shut down the OSPF protocol in the least disruptive manner and notify its neighbors that it is going away. All traffic that has another path through the network will be directed to that alternate path. A graceful shutdown of the OSPF protocol can be initiated using the shutdown command in router configuration mode.
Essentially, the advantage here is that the router that is being shutdown will send out messages to other OSPF routers informing them of the shutdown. Thus, any neighbouring routers with routes that are directed via the router in question will direct their traffic via alternate paths. This allows the rest of the network to re-converge faster than just shutting down the OSPF process.
I hope this has been helpful!
Laz