New method available for the purpose of integration, at least is the reason Microsoft is saying for the availability of this class, and as well in the article says:
[This topic is pre-release documentation and is subject to change in future releases.]
For Microsoft Dynamics CRM Online organizations, this feature is available only if your organization has updated to Dynamics CRM Online 2015 Update 1. This feature is not available for Dynamics CRM (on-premises).
I see good value in here for integration purposes of course, instead of using a Retrieve to see if a record exists or not, and after using the CreateRequest or UpdateRequest methods according if the record exists or not, you will be able to use the UpsertRequest.
In terms of development it will decrease, and i would say that it is a big help, however as Microsoft says, please don’t use this always, it has a cons of course, it is a heavier operation, because inside it is doing the retrieve, and create or update after.
So, for now it will be available in Online and not On Premesis, lets have the fingers crossed for having as well in On Premesis.
Below is the flow of the Request inside of CRM.
Source is below: