Hiya,
The best answer you can get is, that it is dependent on the application running on the server O/S.
The reason that dynamic memory is not recommended for production environments, is that many applications are not supporting it. That is usually seen on memory intensive applications(SQL is an example) or simply because of caching types of functions. (SharePoint
is an example).
The major concern here is when VM's are decreasing the memory for a VM, the application does not understand this. Usually it is not a problem when increasing the memory. - Again it will depend on the application.
Think of it as hot swap memory and how you used to use that in the physical machine days.
Also when there is not adequate memory, operating system will use paging. Paging uses disks and disks has a lower access time than memory.
In general dynamic memory is easier to control than dynamically expanding disks, as you can set the buffer size of the memory, which is still not available for the dynamic disks.
Besides the above, the following links states:
"Workloads that are not NUMA-aware will not take advantage of virtual NUMA. However, the guest operating system may perform some NUMA optimization. Enabling Dynamic Memory (therefore presenting only a single virtual NUMA) should not cause performance
degradation"
http://technet.microsoft.com/en-us/library/dn282282.aspx
