Merger of your private connections and the internet in any enterprise WAN lets you in integrating and managing internet access on low cost broadband along with WAN for internal custom application and data synchronization along with remote office backup. This in turn will enable the network in not sending cloud directed network traffic into the internet and to route it using your private WAN until it reaches the cloud data center. SD-WAN alone can give you flexibility and automation, but for getting the best of your WAN infrastructure you will have to integrate the two for squeezing out the best of both in the form of an intelligent WAN that allows applications to use multiple physical paths between locations, ensuring better optimization and the optimal connectivity for applications.
The lower cost factor of software defined WAN will allow you to depend more on broadband and little on your private links. They would effectively enable you in routing traffic dynamically based on intelligently studying the current state of the network. All this will not only give you a better means in the form of smooth network but also minimize reconfiguration headaches.