External vs Internal tile edges

Not really technical, but I'm looking at this from a programmer's view.
To clarify:

I can see how the external tile edges can help in a topdown game. You won't have to change the characters bounding boxes to make them appear in front of the object.
But cutting the boudingbox's height in half also achieve the same sort of depth.

I noticed that alot of top-down games are using the external edges or a hybrid, and platformers using internal edges.

I was wondering which methods are to be used in different situations and why. I'm currently using internal edges in a top-down game, and it's working out so far. But I don't want to run into problems later on, and have to redo the whole tileset.