One of the biggest achievements of using HADR is that the standby database can be opened in read-only mode and used for reporting purposes. For example, in some hardware replication solutions, it is not possible to open the standby/replicated database. In this way, you can release the primary database from additional processing effort induced by possible intensive reports. Issuing read-only queries on the standby database does not interfere with the log replay mechanism, so it has no impact on data synchronization.
For this recipe, we will run some simple queries on the standby database to demonstrate how to use the standby database in read-only mode.