IBM JVM WebSphere Application Server what is the effect of -XX:+UseG1GC? Does -Xgcpolicy:gencon supersede?

Question

As per IBM link (https://www.ibm.com/support/knowledgecenter/SSYKE2_8.0.0/openj9/xgcpolicy/index.html), the gc policy can be specified by setting by -Xgcpolicy. Default gcpolicy