Title. I would like to be able to move the app to the SD card as my device constantly suffers from lack of free space in internal storage (yes, even ~100 MB of space freed does make a big difference for me).
I'm not sure how exactly it works in Android, but I can see internal storage being freed after I move freshly installed, never launched (so, cache size should be zero) apps to SD, so I assume it does something with apps themselves as well.
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I think I get what you mean now - to make an app movable, the developer has to set a value in AndroidManifest.xml, then the OS itself will offer an option to move that app elsewhere in app settings.