When developing a Sketch it's common for me to trace over reference geometry using Splines.
It's also common to place a Spline point in the incorrect location or place a series of points that wind up appearing a little off.
This is where an Undo buffer during Spline placement would be a welcome feature.
CTRL+Z is the typical key combination in other CAD/Design/3D packages; many of which will let you Undo the entire string of points and then continue with the Spline without exiting the tool and redrawing much of the geometry.
Also, a key combination to close the Spline to the first point placed would be nice.
At present the ENTER key will stop the Spline placement with the last point placed, but this also leaves the Spline open (which is still very useful)
I would suggest that SHIFT+ ENTER or CTRL+ENTER be used to close the Spline "Loop"