Positional Control of X, Y, and Z

In this Question Line video, Jason answers the following question regarding the position control of X, Y, and Z translations: 

We are having a spirited debate about the height of the post in the Z axis. Do we need an additional reference frame for the top of the post? I think since you have a callout to 3 datums, it should be enough to define the positional tolerance in all 3 axes.

Jason walks through the submitted drawing below, explaining what each feature control frame is controlling: 

Jason explains how the datum reference frame has fully defined all six degrees of freedom and established a zero point on the part. He then walks through the drawing, discussing how the posts are being controlled and explaining why the feature control frame for the top surface of the post is essential in constraining the post vertically.  

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