Just as a brief summary for those not familiar with the topic: A vendor of proprietary software can store data in closed, proprietary data formats. Thus, if you are a customer of that vendor it becomes very difficult for you to move to a competitor's product, for example if you like the features or price/performance of that offering better. Instead, the cost of moving, the risk of loosing all your data may be too great. You are 'locked in' to the current vendor...