What is a Power Plan ?
A power plan is a collection of hardware and system settings that manage how your computer uses power. You can use power plans to reduce the amount of power your computer uses, maximize performance, or balance e two.
Power plans available with Windows Server 2008 are Balanced , Power Saver & High performance.
In Microsoft Windows 2008 & Windows 2008 R2 Operating Systems , the default Power Scheme is set to be as Balanced which gives a balance between Performance and Energy Savings.
Doing some research on the impact of Power Scheme on Performance of Windows 2008 Hosts and specifically Hyper-V Hosts led me to multiple articles that has been referred below. Interestingly there is a well documented Microsoft Knowledge base article as well that you can find here. Although the KB does not say how much of an impact can the change have , there are some bloggers who have shared their testing result on the same.
Changing default power scheme from “Balanced” to “High Performance” has yielded 22% improvements in SQL performance that has documented by Glen out here and Improvements in Hyper-V Performance can be found here. In our preliminary testing , we are seeing better results for Performance of Hyper-V hosts that has been changed from default “Balanced” Power Scheme to “High Performance” Power scheme.
For people who are interested in Changing the Power scheme –
In a Full Installation of Windows Server 2008 , Open Control Panel –> Power options and you will be bale to select the Power Scheme of your choice
In a Core install of Windows Server 2008 , One can make use of powercfg.exe command to change the power scheme.
” powercfg -getactivescheme ” would dispplay the active Power Scheme in the Host
” powercfg -setactive 8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c ” use this command to set the Power Scheme to High Performance
We are still doing our round of testing to validate the improvements in Performance of Hyper-V hosts and Windows 2008 hosts due to Power Scheme. Would love to your experience and feedback as well.
Hybrid Cloud Ramblings 
I know this is an old post, but putting your servers at max performance is always a best practice. In production you want to BAN power saving settings. On the physical servers (BIOS) as in the VM itself!