What do you prefer, keeping your Chrome browser open to get notifications about incoming mails, calender and chat or close the browser yet let these services run in the background? There can be many such service which will become more useful if they run in the background and notify a user if there is any update.
There are many useful hosted apps, extensions available from Google's Chrome Webstore which will become more useful if they get the capability of running in the background.
Google has enabled developers to use the power of 'background pages' for their apps available from the Chrome Webstore.
According to Google' developer blog, "Apps and extensions that use the new 'background' feature can continue to run in the background—even if the user closes down all of Chrome’s windows. “Background apps” will continue to run until Chrome exits. The next time Chrome starts up, any background windows that were previously running will also be re-launched. These windows are not going to be visible but they will be able to perform tasks like checking for server-side changes and pre-emptively loading content into local storage."
However, to ensure this will not create a security hole Google has made it functionality available only to apps and extensions, and it can't be used by regular websites. In addition, developers will have to specifically mention that they use 'background' capability on their apps.
It also doen't mean that user will not be aware of what apps are running in the background, users will be able to see which back apps are running using the feature.