According to Google, you'll get a different photo on every screen connected to your Mac, so your ridiculous 5k monitor setup will be more like a posh gallery than a posh desktop work environment. The app only pulls from publicly shared, high-res photos that don't feature people, so you can expect a lot of tranquil nature and soothing landscape photos. Google also helpfully includes the photographer's username so you can track them down to check out more of their work.
If you're on Android, Google's earlier Wallpapers app will also let you set your phone to shuffle through the same set of popular photos on the home or lock screen. And if you're a budding photographer trying to get your work in front of the thousands of screensaver users out there, you just need to follow these guidelines and then post a picture that gets a lot of +1s. If you find yourself short on Google+ friends, Google product manager Neil Inala wrote in his blog post that joining the company's Google+ Create program will also give you a leg up.