One of my former employers recently combined their Plan Commission and Zoning Board of Appeals to gain greater efficiency and reduce staff and management costs. One benefit I've seen in some places was that a site plan approval is required by a Plan Commission but any variances associated with that plan must be approved by the Zoning Board of Appeals. This type of setup can add unnecessary complication to the process as well as potential unpredictability.
Who has been through the process of combining such Boards/Commissions? What types of political or legal issues arose?