Just so no one is getting confused. The flat left wrist is used for clubface alignment (and the thrust direction as well). Go to impact fix and check your alignment. Its by far the most dependable checkout you can make in that respect. Now...the EXACT direction the left wrist is facing may be different from golfer to golfer, but it is absolutely used for clubface alignment. The other being the trail forearm facing down the line (or cross line) at impact.
That is why Homer says to go to impact fix, verify alignments and THEN MONITOR THE HANDS. By monitoring the hands, you dont need to worry about the clubface or clubhead you just monitor the hands and take them to the same location established at impact fix. Hands ahead, forearm on plane, flat left wrist facing out to right field....
Brian is saying whatever your alignment is at impact fix is the alignment it should be at impact.
-Patrick