The feature allows to disable triggers on the target database so there are no issues when replicating, especially when copying existing/old data.
Will be useful to everyone that wants to migrate a database with 0 (zero) downtime and keep both copies running until migration and connections are fully moved to the new database or even keep two copies running for Multi-Master config.
It should work by using a specific role created by DigitalOcean to allow replication, it's how it's done in Amazon RDS, they implemented a role called "rds_superuser" that can be granted to the user in the target database - check what it allows for here: https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Appendix.PostgreSQL.CommonDBATasks.html#Appendix.PostgreSQL.CommonDBATasks.Roles - it allows one to set the session replication role.
This new role should be in all new databases and when granted, it may allow to lift a few other superuser limitations that I've seen a few people requesting in DO's forums.
Session replication role is a feature available in PostgreSQL since version 9.3:
Amazon implemented it in 2014: