We have an on-premise deployment. After all, it is an email client. The way you use Microsoft Outlook or any other email client it makes sense to be deployed on-premise. They do have a SaaS version. The way it works when we are working on an enterprise laptop — the laptops that the company has provided us — it is installed on our systems. Other than that, the particular tool or email client can also be accessed via web login. We often use that when we are using it from a smartphone or any other non-company device.
Our primary use case is just what it is: an email client. It is my stable solution and the only email client that I use. Web meetings are also a part of what we use it for. They have a solution — their adjacent solution is called IBM Sametime or HCL Sametime — which is the chat functionality. But our primary use case is as the email client.