One distinct advantage of adopting a proactive approach as opposed to a reactive one is that organizations are more assertive in being able to define their own identities. Reactive approaches tend to leave organizations in a state of responding to change and conditions as opposed to making a statement regarding such realities. Proactive approaches are ones in which organizations are able to assertively make statements and design their actions in accordance to their visions and missions. Proactive approaches show that organizations believe in what they are doing and how they adapt to changing dynamics. While reactive change paradigms might communicate this, it is not as deliberate and assertive as with proactive change approaches.
I tend to think that another advantage to adopting a proactive approach is a greater chance of troubleshooting problems that might arise with change. Reactive approaches are, by design, responses to change. Proactive approaches are statements and actions that seek to understand the nature of change and seek to appropriate it into an existing model. Problems might arise with either approach because change is sometimes unpredictable. Yet, proactive changes are more visionary in nature and are able to better understand the nature of change and account for challenges more than reactive approaches.