Back in 2006 I wrote whitepaper outlining my thoughts about running Citrix XenApp virtualised in a ESX VM. The information is probably still relevant so if you want to read it Click Here > Running XenAPP in vSphere (6604 downloads)

Recently I had a conversation with someone from VMware and we agreed that: there’s no need to remove vmmemctl, as installing it will not have any negative impact on the VMs by itself. Even if you do not plan to over-provision your ESX hosts in terms of memory, it is in your best interest to have the Balloon Driver as an insurance should memory pressure increase (i.e. because of a host failure and HA restarting VMs on the remaining hosts). If vmmemctl is not installed, ESX will have no other way than to reclaim memory by swapping out Virtual Machine memory, which will be a more severe performance impact. Here a somewhat recent post by Scott Drummonds on that topic: http://vpivot.com/2009/09/25/esx-memory-management-ballooning-rules/”