One of the big advantages of using Oracle VM Server for x86 or SPARC is the ability to migrate virtual machines. If two Oracle VM Servers are grouped together in a server pool under one Oracle VM Manager, you can perform a live migration to move an Oracle VM to a new server without shutting it down. This can be handy if you need to perform maintenance on one of the Oracle VM Servers but want to minimize the impact.
We've put together a How-To that walks you through a live migration of an Oracle VM and explains the prerequisites and roles required. It also gives you a pointer to some additional resources - the Feature Reference Guide has chapters about Oracle VM Servers for x86 and Server Pools, and the How-To library has a few other How-Tos that relate to VM management.