Autonomous transaction like oracle in pl/pgsql
Add this feature for implementing logging in procedure/function.
Darren Duncan commented
In a more general sense, autonomous transaction support is valuable because that goes a long way to being able to support a multi-process virtual machine in a DBMS, where one can effectively start a new "database connection" working parallel to others, but this is started by code within the DBMS rather than having to be by code externally. So good for computational completeness.