That's true but there are peculiarities. People usually don't do it on Windows VMs for instance. I myself do not use it at all but prox also does KSM (Kernel S

That's true but there are peculiarities. People usually don't do it on Windows VMs for instance. I myself do not use it at all but prox also does KSM (Kernel Samepage Merging) which activates when RAM usage is at a particular configurable level and helps a lot more than ballooning especially if your VMs and internals are similar.