Question:
Why is Android Support Repository needed? What does it do and contain?
Answer:
Android Support Repository – A local copy on your computer of the Maven repository that contains compiled versions (.aar) of the Google support libraries (such as support: appcompat , support: design , support: v7 , etc.)
Located along the path: \Android\Sdk\extras\android\m2repository\com\android\support
It is used for offline work of the IDE and speeding up the assembly of the project, since in this case you do not need to download these libraries from the Internet, when they are needed in the project, it gets them from your computer.
If you don't use any google support libraries, then you don't need a local copy of the repository, however in modern android development it is difficult to imagine an application that does not use these libraries.
Android Support Library – A local copy of the source code for the Google support libraries.
It is used to actually see how everything works there, copy resources for customization, make custom views based on support library widgets, etc.