RDS provides two backup methods: Automated backups and user-initiated DB snapshots. Automated backups are initiated during the creation of an RDS instance. You set the backup window and the retention period for the backups and you’re ready.
Although automated backups seem attractive because they are easy to manage, they have some constraints.
1.   Retention: There is a 35-day retention period limit. After exceeding that limit, the snapshot is then deleted.
2.   Deleted database: If you accidentally delete a database for any reason, automated backups are going to be removed too.
3.   Disaster Recovery: Automated backups can only be restored from within the same region.
If you have a DR strategy, you might want to move the snapshots between multiple regions.
These 3 constraints can be resolved with the DB snapshots.
1.   DB snapshots can be retained for as long as you wish. Means RDS manual snapshots will only be deleted when the admin specifically deletes the rds snapshots.
2.   DB snapshots are not removed if you accidentally delete the database.
3.   DB snapshots can be moved from one region to another without any constraint.
Amazon Web Services gives us three ways to take manual DB Snapshots: the management console, the awscli command line utility and the various Amazon SDKs.
As long as manual snapshots are taken regularly and kept secure, it’s easy to recover your database within a few minutes. Ultimately, you have to pay for the backup storage that you use until those backups are deleted. In order to really enjoy RDS manual snapshots, it is best practice to automate manual snapshots to serve your database backup policy.