One of the things I liked about Mongo (compared to Postgres) was the ability to configure a list of connected servers, an election pattern for deciding the master, and... that's it. With that, servers on multiple hosts were load-balancing read-only queries, propagating writes, and failing over in a way that worked for us (a few seconds of write failures of the master ever died was fine for the application we were making).

Meanwhile, postgres has this replication scheme available ("Trigger-Based Standby Master Replication") but the steps to implement it were much harder, and required an evaluation of possible replication/failover needs that we didn't know enough to do. It also requires a dive through pages of the documentation at https://www.postgresql.org/docs/10/different-replication-sol... to understand how to implement any of the above strategies.

Postgresql's availability of different replication methods, and the resources available for each, are impressive for sure. But there's something to be said for having Mongo's easily-understandable list of steps to get multiple servers talking to each other right away.