This can have a big performance impact, as unless there are a large number of elements parallel streams are significantly more expensive than non parallel ones. I see it being used in:

org.jboss.as.ejb3.remote.AssociationImpl#registerClusterTopologyListener
org.wildfly.elytron.web.undertow.server.ElytronAccount#ElytronAccount
org.wildfly.elytron.web.undertow.server.ElytronHttpExchange#getRequestParameters
org.jboss.as.security.remoting.RemotingConnectionCredential#RemotingConnectionCredential
org.jboss.as.security.api.ConnectionSecurityContext#getConnectionPrincipals