If you are talking about from a phone to a tablet then that does not always work out as planned, especially if there's a lot of edittext boxes and labels involves.
When designing you should use anchors as much as humanly possible, you will also need to create some designer script too.
But at the end of the day it completely depends on multiple factors. If you are creating a game then I believe that automatically scaling is not too bad, but if you are creating forms, I would most probably go for 2 layout files just to be on the safe side and for speed of development. Create one layout, get it exactly the way that you want with code, then create another layout using the first one.
You might be able to autoscale everything using one layout, but I doubt it especially if you are using labels and edittext boxes, oh yes and don't forget about text size.
You're probably better of using 2 layouts, but I'm sure someone else will give you a completely different answer.