The current behaviour in Sketching is for new curves to be merged within whichever Sketching browser layer the sketch was made. Oftentimes, users need to be able to select a curve/profile and assign it to its own selectable layer in the Browser. Either this can be done by a global "One layer per sketch curve" mode, or if that threatens to make the sketch folder too large, have at least a menu function available that splits whatever is selected in its own layer.
This principle could be applied to parts of bodies as well: Select faces you wish to turn into an independent model in its own layer, ansd the system splits the model accordingly, healing faces along the way.
