Despite being not recommended, many users still run Hadoop ecosystem programs from the Shell Action (e.g. hive, beeline, sqoop, etc), even though we have Actions for those. One of the common problems we've been seeing here lately is that HADOOP_CONF_DIR is inherited from the NM, and is pointing to the NM's copy of the Hadoop *-site.xml files, which is often not well suited for client programs. This can lead to all kinds of weird problems, such as permissions errors, missing logs, etc.
As a workaround, we've been telling users to set HADOOP_CONF_DIR to /etc/hadoop/conf, however, this has some disadvantages. Ideally, these client programs should pick up OOZIE_ACTION_CONF_XML instead. Given that OOZIE_ACTION_CONF_XML is an amalgamation of all of the Hadoop *-site.xml plus things Oozie and the user set, we can simply have the Shell Action copy-paste it to the correctly named *-site.xml files, and point HADOOP_CONF_DIR to there.