The Memory Buffer setting for Dynamic Memory can be thought of as a memory reserve for the virtual machine. For example, if you configure the buffer to have a value of 50 percent, an additional amount of memory of up to 50 percent of the committed memory can be allocated to the virtual machine when needed.
One common scenario where this can provide benefits is when the virtual machine is running a workload that makes heavy use of the disk cache. In this case, increasing the buffer setting will result in additional memory being allocated to the virtual memory from the pool of idle memory on the host. For such scenarios, begin by raising the buffer setting from its default value of 20 percent to something like 30 or 40 percent and observe the change in the performance of the workload. Then if additional tuning is required, try raising the buffer setting a little further. Just don’t suddenly bump it up to 300 percent because you might end up starving the other workloads on the host!
The above tip was excerpted from Mitch Tulloch's book Training Guide: Installing and Configuring Windows Server 2012 from Microsoft Press.
Mitch is a nine-time recipient of the Microsoft Most Valuable Professional (MVP) award and a widely recognized expert on Windows administration, deployment and virtualization. For more information see http://www.mtit.com.