[Yoda]

10-9 A says the left wrist should be Bent/Level/Vertical Why should it be level, what are the issues of it not being level?

Correct Timing demands that the Ball be struck near -- but just prior to -- Full Extension (of the Swing Radius, i.e., the Left Arm and Club). That Full Extension (2-P) is a Perpendicular Motion that occurs just past Impact when the Left Wrist is fully Uncocked. The Level Left Wrist -- top of Left Forearm in-line with the first forefinger knuckle -- is the 'central' alignment of the Perpendicular Motions (Cocked, Level and Uncocked). Incorporating this alignment into your Impact Fix (8-2) and Address (8-3) assures (1) the correct near-Uncocked condition at Impact; (2) offers a great sameness to all your Golf Strokes; and (3) serves as a ready visual check of the correct Perpendicular Impact Wrist Condition.