For me it's been the ease of use and reliability of the system. Installation and setup of our initial hosts were straight forward and then from there the ability to scale up across the infrastructure we created with such speed was definitely miles ahead of OpenStack (our first attempt at a private cloud) at the time of setup.
Our aim has been to have our own AWS type infrastructure alongside it.
I think there's some work to do with managing configuration of underlying hosts. It would be nice to have a faster route to scaling up and provisioning interfaces.
If you want a straight forward access to a private cloud based IaaS then we have had very few issues scaling the VM and provision side of this product.
Quick fire ability to scale our infrastructure as our application demands through automation.
We had a lot of spare hardware that has been put to good use, instead of gathering dust it's helping us use every ounce of spare CPU cycles where needed.
Less management through automation.