Installed web apps become "permanent" features in the Chrome browser experience. As users' expectations shift and apps become more and more important to users' experience with the platform, users will "think in apps" and search them out and install them. Installing an app ensures it is launchable from the New Tab page (aka Chrome Apps Launcher), and can take advantage of additional abilities such as unlimited storage. Installed apps are easier to access and run. Plus, the concept of ownership is powerful for users.