Interesting detail from GSMArena:
So finally an answer to all those low-end devices with inadequate internal storage but having an SD slot (though it sounds like you lose the portability of the card between devices as the downside). Now if only the manufacturers will update them to M...Adoptable storage devices
Users can now add an SD card, which will then be adopted by the system to behave like internal storage. The memory card will be formatted and encrypted and will be seen like internal memory. You can then install apps and other private data easily onto the memory card.