a stand by database replica like AWS RDS offers it, in case of the master failing, the traffic can be redirect to the stand by replica. This can also reduce the downtime during updates.
Another use case, to point metabase or any analytics style server/dashboard at it. This would be parity with Heroku as well.
@Avi Moondra: Totally agree with you. You don't want reporting systems hitting the main database. I use read replicas on DO specifically for Metabase