Thanks for a quick reply,
Honestly I have no answer to why "reserve all memory", this is a request from the guys developing the applications that are running on those VM's. I'll check how they justify this, as you point out we have more than enough RAM on the host.
However, it can't be by design that guests with reserved memory generate "critical" alarms?
And what problems can the reserved memory cause HA? All hosts that are in HA clusters have capacity to solely run all VM's in that cluster.