Undoubtedly the SharePoint 2013 App Model sounds promising. Now you can develop SharePoint Extension as an App for SharePoint. The client object models have been greatly expanded. Now we can explore more custom business logics to work with SharePoint without the fear of security related issues. Some APIs in the SharePoint server object model are not available in the client object models. These are almost entirely administrative and security-related classes. Custom SharePoint logic that addresses these areas is more appropriate for a Windows PowerShell extension or classic SharePoint farm.
Some of the added advantages of Apps for SharePoint are :
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