Employee Control is a powerful feature in Core that allows you to control every employee's access to activities, expenses and projects throughout the program. It ensures that confidential data is not accessible to employees who should not see it. Though it seems similar to Project Assignments, Employee Control is a security feature that applies to all screens, reports and functions in Core and not just time and expense entry screens. That is why it takes precedence over the project assignments if both are implemented simultaneously and there is a conflict.
In Employee Control, you assign projects, activities and expenses to employees. Check the Core Help for details.
On the other hand, in Project Assignments, you assign employees, activities and expenses to projects. Project Assignments apply to the time and expense screens only.
The best use case for this is a company with multiple offices. Employees of location A are assigned projects belonging to location A and they get to see only those projects throughout Core. This can be accomplished by both features. However, there are businesses that have hundreds of projects. Assigning project to employees (Employee Control) is easier for them as compared to assigning employees to projects (Project Assignments). Check the Core Help for details.