Java tweaking to use Flags or not to use Flags?

I'm starting to think with everything floating around that might be better to let Java handle everything... There is to many of these try this try that but has anyone actually benchmarked or proven that any of the flags besides of course giving more ram do anything good?

This is pretty much all I run..

jdk1.7.0/bin/java" -d64 -Xincgc -Xmx12G -jar craftbukkit-0.0.1-SNAPSHOT.jar nogui

Any advice would be good.