Postgres 10 Backup: Should I run the backup in the master or in a slave? I have been using the continuous-archiving and Point-in-Time Recovery for backing up my postgres 10 DB https://www.postgresql.org/docs/10/continuous-archiving.html, however, the master database is handling a lot of work load and my slaves, that are read only, are not that busy, so, am wondering:

Is there any difference in running the backups in the master database than running them in one of the slaves? 

I create two backups daily, so, I'm confident that it might be one of the reasons why the master database is experiencing much more workload than the replica ones.
You can run pg_basebackup against the slave server just as well as against the master.