Freehand tool smoothing preview Option

[steve.ledger]

It's surely a solution but would generate a billion control points

Excuse my confusion but because you mentioned ;

....... just seeing the line you trace, dealing with the smoothing slider afterwards if necessary.

I saw the solution as getting your wish
So, zero the smoothing slider, see your line then select the shape tool and deal with the smoothing afterwards. This will reduce the 'billion control points' to something more manageable yes?

..and also mean adjusting and resetting the slider at every stroke.

Are you sure? Certainly not for me. Once the smoothing slider is set to zero, all new strokes in the document are zero smoothing.