In 5.7 the landscape deformation tool received some changes. Landscape splines now require their own edit layer. I think the goal was to force the workflow to be non-destructive before it is committed and the layers are merged (Collapsed).
@Epic In some use cases this adds friction to the creation process. Can we please get an option to use the base landscape layer with our splines?
An example of how this adds friction. Lowering a road significantly and smoothing the terrain around to match it. The new process requires dozens of repetitions of (Spline deform> Merge> Smooth base layer> Create new spline layer). Previously you could do it in 2 passes (deform> smooth> deform> smooth).