Microsoft delivers the latest Windows security and user experiences updates monthly. Updates are modular meaning that, regardless of which update you currently have installed, you only need the most recent quality update to get your machine up to date.
With the fast pace of Windows security and quality fixes, distributing this large amount of updated content takes up substantial bandwidth. Reducing this network transfer is critical for a great experience. Moreover, users on slower networks can struggle to keep their machines up to date with the latest security fixes if they cannot download the package.
This is the kind of grunt work that doesn’t get flashy slides in a presentation or a mention in a commercial, but it’s awesome work nonetheless.