Fred Wilson venture capitalist and Co-Founder Union Square Ventures
“The Board Chair runs the Board of Directors [and] is a Board member with the same  responsibilities as the other Board members. [He also ensures the Board functions:] [meeting regularly], [getting the CEO what he needs from the Board],[ensuring all members contribute], [and giving the CEO a single contact on various issues]. 
Small boards (three or less) don't really need Board Chairs.  At [seven +], [Wilson] believe[s] it is critical to have a Board Chair.”
Although common, Wilson doesn’t believe the founder/CEO should also be Chair. “ [Wilson] think[s] the Chair should be an independent director who [helps] the CEO manage the Board.
 When it works, the Board Chair role is hugely impactful. It allows the CEO to spend [his] time  running the business and not worrying about the Board.” Fred Wilson, The Board Of Directors - The Board Chair, Mar 19, 2012; http://www.avc.com/a_vc/2012/03/the-board-of-directors-the-board-chair.html