The decouple feature has been added to the Platform to enable customers to detach the application from the OutSystems Platform in the event that they decide to cease using the Platform and maintain the native .Net or J2EE code in those technologies.
The OutSystems Platform is layered on top of standard application server environments like .NET or J2EE. The application visual models designed with Service Studio are compiled by the Platform into standard, well architected, native applications which are then deployed on these Application Server environments. The generated applications are architected as native applications which can run independently of the Platform proprietary services. No runtime interpreters or proprietary closed libraries are used.
This means that if you decide to remove the OutSystems Platform from your environment you can detach the applications native source code and deploy it in another environment running only the application server.
If an application is detached from the Platform, you lose the benefit of dynamically monitoring, managing and changing (ECT) application in production as well as all the other features of the platform.
Nevertheless this feature is quite uncommon in the software industry, allowing you to run and mantain your application after ceasing the use of the Platform.
Check the following Technology Independence Document for further details.