When my UWP app builds, it goes into the output path of the current project. Inside this, there is always an additional folder called "AppX" that contains duplicates of everything.
When the same app installed from the store, there is no AppX folder associated with it.
Why is there this useless folder of duplicated data when developing?
With Visual Studio 2015 Update 3, we have added the option for developers to specify the layout path for their UWP apps. This determines where the package layout is copied to on disk when you build your app. By default, this property is set relative to the project’s root directory. If you do not modify this property, the behavior will remain the same as it has for previous versions of Visual Studio.
From MSDN source.
This folder will be generated when deploying and debuging. It actually is your app's debuging installedLocation path. You could use Package.Current.InstalledLocation.Path to test. The debuging app's installed location would be like this:
D:\App170221\AppPackage\bin\x86\Debug\AppX