This is very unusual and not documented anywhere by VMware but this came from a VMware support engineering working an issue where a customer's vMotion was failing at 82%.
The only errors were:
After exhausting all likely troubleshooting scenarios and options (resetting luns, restarting agents, rebooting guest) it was discovered that this non default value had been changed in all the VM's that were not able to be vMotion'ed. The only way to see this value in the vSphere client is when the VM is powered off then in Edit Settings select Options -> General -> Configuration Parameters
The solution was to change this value to a larger value such as 20960. Make sure to remove the VM from inventory (after powering it down) then readd to inventory to make sure the vmx configuration size change is read into vCenter server.