Besides what everyone else said, the obvious advantage is the latter builds in the logic for exiting the loop once getNext has run out of elements in the slice/map. Your former example will need a final step that's like:

    ...
    if getNext() == nil {
      break
    }
    ...

This isn't a huge boon, and is mostly a matter of style. But I prefer the latter because it's logic that gets handled with the range builtin, so my code can be more about application logic, rather than muddling in breaking out of loop logic.