For example, a department may be in the process of developing a new application. They receive new versions several times a week, and each version needs to be installed before it can be tested. It is extremely inefficient for the administrator to have to do this each time. Instead, you can enable User Installed Applications with Access Control set to specific people in that department, and Workspace Control set to a Workspace Container that holds the computers in that department. As a result, the specified users can install the updates on the specified computers.
Similarly, a small number of people might use a highly specialized software package such as AutoCAD. They may well know more about the software than the administrator does, and so it makes more sense to allow them to install the AutoCAD updates or extensions themselves.