Why is it that apps use space on both the SD card and internal storage?

[paperdoctor]

I have a Moto G 2nd generation, Android 4.4.4 rooted.

There are several large apps that I would like to store on the SD card, but even after moving them to the SD card, they still appear to be taking up space on the internal memory. It's as if there are duplicate files on both the SD card and internal storage.

How do I free up space on the internal storage?


Edit: included screenshots

 

[Rukbat]

What you see in main storage is a symlink (symbolic link) to the app on the SD card. Linux (the OS underneath Android) is set to look for apps in internal storage. When you move them to the SD card, there has to be something in internal storage pointing to where they are on the SD card. That's why you don't save much storage by moving apps to the SD card. (It's not designed for apps, it's designed to store data - media files, documents, etc. They don't need symlinks, because the apps that work on or with them can be told to look on the SD card.)