Manually removing and sorting Usings can become a tedious process when working with many classes and files. Handle this automatically when saving any file in Visual Studio 2017 using the Productivity Power Tools 2017 extension bundle installer, specifically the Power Commands extension. These can be installed directly by navigating to Tools | Extensions and Updates … in Visual Studio.
After installing the extension, go to Tools | Options | Productivity Power Tools | Power Commands. Check Remove and Sort Usings on save.
Test this by editing a code file and saving (Ctrl+S). Any unused Usings should be automatically removed and existing ones sorted.
For ReSharper users, there is a chance that this setting does not work. This is a known issue. As a work-around, deselect Hide overridden VS menu items in ReSharper options.
Navigate to ReSharper | Options | Environment | Keyboard & Menus. Uncheck Hide overridden VS menu items.
The Power Commands extension should be working again.