When running in a virtualized environment like z/VM it's beneficial if the hypervisor knows if a server is idle or not. Usually this is implemented by waiting a certain time before considering a server truly idle. The problem is that many of the applications and middleware products do housekeeping tasks way too often for this to be really effective. So any effort to lower this "noise" is good. The updated whitepaper "WebSphere Application Server - Idle Server Tuning" provides tuning suggestions for a Websphere environment to reduce this noise.
On top they also provide tuning recommendations to reduce the startup time. The team updated the paper to cover WAS v8 and v8.5.5 including the Liberty profile.