The new thing here is that your PC will be able to not only grab the updates from other PCs in your local network but also from other PCs on the Internet. In the first case the potential for bandwidth savings for consumers and businesses with multiple PCs is pretty big while in the latter case it's mostly Microsoft that benefits. We're not sure how this is going to play out as there are still a lot of people out there with strict bandwidth caps so P2P delivery of Windows Update may not be desirable just yet.
More specifically, you can choose where to download the updates from, including your own local network or PCs on the Internet, and of course you can turn off this functionality.Source: Neowin
This is an interesting move from Microsoft as this can potentially speed up the delivery process for updates and at the same time, it can reduce the strain on the company's servers too. For Microsoft, it's a win-win, but for consumers, it can mean that you are giving up a bit of bandwidth to support this functionality.