[SAPUI5] Extension vs Adaption Project

I was wondering for quite some time, what the difference is between Extension Projects and Adaptions Projects. In the comments to this blog post, I finally found the answer from Oliver Graeff:

Adaptation projects are one of the capabilities of SAPUI5 flexibility, which lets developers, key users and end users adapt/extend SAPUI5 applications. Adaptation projects are the go-to solution for developer adaptation in SAPUI5 and are the ‘next-generation’ extension projects. Using the concepts of SAPUI5 flexibility, adaptation projects offer many more possibilities, such as extending SAP Fiori elements applications or extending apps without pre-defined extension points.

To check for a specific application, what the recommended extension approach is, simply go to the Fiori Reference Library, search for your app, choose the backend system (S/4 or Business Suite) and the current release version, navigate to Implementation Information and expand Extensibility. For example, My Overtime Requests on S/4HANA can be extended via an Adaption Project.