Tweaking battens beyond end points can in some cases produce a more fair curve.
There is one restriction though, ask yourself is there a physical structural entity in the end object to support such a curve?
In the case of waterlines, sure, these are hypothetical and have nothing to do with structure, so tweaking if required, is good in this case.
Buttocks and diagonals do however have something to do with the structure ( ie frames and planking ) so never tweak the battens beyond these lines. There is nothing structural beyond the edge other than air/water that can support this shape.