[hodgesrm]

Indeed--anything where you want the secondary to be other than a bit-for-bit copy of the primary. It's also convenient for HA in some cases due to the fact that the DBMS copies are fully independent, hence free from propagated bit-level errors and also available for unimpeded reads.

MySQL started with logical replication very early on and it has proven extraordinarily useful. One of the more interesting use cases is feeding log transactions into data warehouses, which should be possible in PostgreSQL 10.