Developers can build, test and publish their apps here. Here you can deploy apps for SharePoint from Visual Studio 2013 to the developer site and you don't need to create an App Catalog site since the developer site template by default creates an App Catalog library. The developer template is available under the collaboration site template. 

How to create a site using this template

web application

Why create an app?

If you are planning to do remote development/deployment like in the cases were VS2012 / VS2013 and SharePoint 2013 is not installed on the same computer you will be needing a root site collection created using Developer Site Template. (If VS2012 and SharePoint 2013 are on the same computer this is not a requirement).
  1. What Remote Development and Deployment?
    Yes, you heard it right VS2012 and VS2013 support the deploying of sandbox solutions to a remote SharePoint site. When you create a SharePoint 2013 Project using VS2012/VS2013, you will get an option to publish to a remote SharePoint Site when you right click on the SharePoint Project as shown below:

    display as a sandboxed solution

    Remote Publishing from Visual Studio 2012

  2. Publishing App in App Catalog
    Upload the app file to a Developer Site of SharePoint 2013 in the “Apps in Testing” Library.

    app demo