And it was a very bad idea to do this on the Fairphone 2, too, as quite a number of users found out the hard way.
You would willingly hand over the integrity of your whole internal storage to the whims of a flimsy SD card.
If the card decides to stop working somewhen (and they tend to do that), your whole internal storage could be corrupt all of a sudden and you could be in for setting up your phone again from scratch.