The DXA comes with a Core module, with example schemas and templates used to build the example website. This is a useful reference, but many DXA implementation will not make use of these and they will normally be deleted to prevent them being accidentally used, or confused with similarly named items in the customer's implementation.
The problem is, that when running upgrade scripts, these schemas and templates will be imported again into the CMS, and thus need to be deleted again (which is a painstaking process due to the interdependency of items). The other option is to use content porter to handpick only the framework items to import, but this is error prone and also has dependency problems (see https://tridion.stackexchange.com/a/18575/54)
It would be great if there was a further install/upgrade option "framework-only" which only imports the DXA framework and not the core module.
See also Github issue: https://github.com/sdl/dxa-content-management/issues/24