This option joins any stroke with an end near the actual stroke. Now it is not limited to the last stroke, any stroke in the same layer for the actual frame can be joined. The join can join two strokes drawing a third stroke.
If the end and the start of the result stroke are very small, the stroke is changed to be cyclic automatically.
There is a limit distance to join the stroke, if the distance is greater than this value, the strokes are not joined. Actually, a constant, threshold distance is used, but we could expose as a parameter in the UI.
The tool can be used with freehand drawing (Note: UI in the videos is outdated, but the functionality is the same) :
or Primitives:
