Ubuntu OpenStack

The well-suited scenarios where Openstack is well suited when your client or organization is wanting to have its own private cloud built within its own premises to have full control of its own highly secure data of its own clients or employees. I don't see many inappropriate scenarios where OpenStack cannot be used. It definitely is as good and as powerful as any other commercial cloud platform in the world.

It's really well suited if you are looking to implement your own private cloud for an affordable price. Definitely, the best choice if you can't afford to pay for more expensive services and tools like VMware which require pricey licenses. Having Ubuntu OpenStack open source makes it even better for the community. If you don't know how to manage your own infrastructure well or don't have the capacity, you would be better off using some other service.

Ubuntu OpenStack is well suited for startups where there are very tight financial constraints. As Ubuntu OpenStack is open source, the startup organizations will not have to spend a lot when compared to their commercial offerings in the market.
Ubuntu OpenStack is less appropriate in organizations where they don't want to have private on-prem clouds. As deploying a private on-prem cloud is a very cumbersome and tedious task, the organizations must have a dedicated team to manage such on-prem deployments.

If you need to support diverse infrastructures then you need OpenStack. Also if you can't afford to pay costly licenses for commercial products then it is a no brainer. If you need to quickly recover for failures OpenStack will provide self healing and automatic load balancing! Don't use it if your hardware is homogeneous.