Can someone explain the use case behind using a "Sales Cloud License" plus a "Feature License" by ticking the "Service Cloud User" under the user account VS simply buying a "Service Cloud License"?
Is the Service Cloud User tick box a recent addition to the Sales Cloud as I haven't seen this tick box except in a Dev Org?
The 'Service Cloud User' box has been around for quite some time. This is the permission that a user requires in order to get access to a console app. You wouldn't see this box if you don't have a license which gives your org console access. Developer orgs get this box because they have lots of features enabled to allow you to do thorough testing and development.
Originally the console was only for service cloud, which is why the setting is named this way. Now that the console is also available to Sales Cloud licenses we see things like permission set licenses 'Sales Console User'.
If you've got questions about your org's licenses and setting up console, it's probably best to reach out to your AE for assistance.
