Why use jboss-service.xml does it affect in clutered envioro

[shetty_ritesh]

I am integrating the Jboss with IBM MQ. The link below is used to implement this.
http://wiki.jboss.org/wiki/UsingWebSphereMQSeriesWithJBossASPart3

It is written that the <mbean code="org.jboss.naming.ExternalContext"
should be placed in the jboss-service.xml
My question is what difference will it make if i place it in the ws-ds.xml