It's common for companies to develop patent portfolios mainly for defense. Say you build a product, maybe VR goggles, and you legitimately infringe someone els

It's common for companies to develop patent portfolios mainly for defense. Say you build a product, maybe VR goggles, and you legitimately infringe someone else's VR patent, because that's pretty much unavoidable these days. The owner of that patent is in the same VR space, and decides that you're a threat to their business, so they decide to file suit on this patent you've infringed and make your life difficult. But! You've been developing your own defensive patent portfolio around VR, because that's the business you're in. In this case, it's common to find that your competitors are also infringing some of your patents, because you're all working on the same thing. When this happens, it's easy to cross-license -- I'll let you use some of my patents if you let me use some of your patents. Patent problem avoided. This is Microsoft allowing you to use part of their patent portfolio for defense in this way.