You’d do that to colour skin lines differently from hair lines, clothes lines, etc. The paint spreads until it meets a border. I think the Repaint Brush was conceived for traditional animation to complement the Repaint Bucket, which allows to colour a line with a click or selection. You can use this mode to paint tones or highlights onto your character.”
It also automatically flattens each of its brush lines so it does not add new brush lines on top of existing ones. “ The Repaint Brush is used to repaint zones that have already been painted, it will not affect empty zones or pencil lines. You may or may not have read this from the manual: If I am correct in my understanding of this tool, I believe Toon Boom should have disabled the button when textured brushes are selected to avoid confusion.
You could utilize this “repaint” option for its precision as opposed to the general fill effect of the Repaint Bucket. IOW it limits the area being repainted to a brush stroke shape. It is a tool that merely adds a stroke of paint to areas already painted and being such it does not access the full range of brush options. As I understand it (or not), the Repaint Brush Mode is not a tool meant to recolor or replace brush styles as I believe you are considering it to be.
