They are various scenarios in which you may want to restore the DB instance from the previous backup. These include: that you want to test a new DB instance class for your workload, or see how a DB instance performs with Provisional IOPS or you want go back in time and review some of the table data, or your developer wants the latest data from production to test the application. On RDS, restoration is simply a click away. You just need to know the snapshot ID that you want to restore and spin up the new DB instance. Note that you cannot restore a DB instance to the existing DB instance. You have to spin up a new DB instance using the snapshot.
The Restore-RDSDBInstanceFromDBSnapshot cmdlet lets you create a new DB instance from the DB snapshot.
PS C:\> Restore-RDSDBInstanceFromDBSnapshot -DBInstanceIdentifier "copymywebappprd" -DBSnapshotIdentifier "...