You cannot dismiss arguments as marketing-speak just because they don't fit your high-performance viewpoint, and "marketers" have made similar arguments in the past.
The first two paragraphs are about one benefit: using otherwise idle resources. At my lab, we have five powerful servers for data-processing experiments and non-time-critical analytics. Most of the time they sit completely unused. By installing Xen and running things in virtual machines, we have been able to also put tens of differently configured web servers for various small projects on each.
The third paragraph is also very valuable from experience. It has been very useful to keep documentation around how different servers are set up, and verifying that the actual setup still matches the documentation. This has been easiest to ensure by having scripts that create a new VM, install packages and make configuration changes - if in doubt, completely delete the VM and re-create it from scratch with a single command-line.
The first two paragraphs are about one benefit: using otherwise idle resources. At my lab, we have five powerful servers for data-processing experiments and non-time-critical analytics. Most of the time they sit completely unused. By installing Xen and running things in virtual machines, we have been able to also put tens of differently configured web servers for various small projects on each.
The third paragraph is also very valuable from experience. It has been very useful to keep documentation around how different servers are set up, and verifying that the actual setup still matches the documentation. This has been easiest to ensure by having scripts that create a new VM, install packages and make configuration changes - if in doubt, completely delete the VM and re-create it from scratch with a single command-line.