With gaming having its own voice on the senior leadership team, essentially, Spencer will have a little more room to maneuver moving forward.
Previously, for larger projects and sign-offs, the Xbox team would've had to seek the blessing of both Windows chief Terry Myerson and, thus, CEO Satya Nadella before any action could be taken. Myerson likely sees everything through the lens of what benefits Windows, rather than gaming, not specializing in gaming himself. It's quite easy to imagine how he could've potentially hindered important decisions.
One of the reasons the Windows 10 Store is so atrocious for video game delivery is that it's handled by the Windows team, rather than the Xbox team. The Xbox Store has no issues delivering larger files, unlike the Windows Store, and it enjoys much better categorization and usability. There are multitudinous issues with the Windows Store for gaming, but as a quick example: Forza Horizon 3 last year suffered the same download issues that Forza Motorsport 7 suffered from these past weeks – a year on, and still no fix. It's a basic example, but it just doesn't feel like gaming is a priority for Myerson's Windows team, so it's easy to imagine how this attitude could've hurt Xbox.