Base is meant to be a set of features that will provide the "lowest common denominator" for building Drupal apps and distributions.
If you've ever installed an app, you might have found out that, while you want to keep the fields and the content type provided within the app, you might want to completely change the view provided with it or the contexts. Base will give you a content type, default fields and user permissions, but will never assume anything on how you want those fields displayed, where in the menu you want to show them, which URL they should have etc...
That way, we hope that Base can provide as much interoperability as possible between Drupal apps and distributions (by using the same field names, roles, content types etc...) without forcing the site builder in displaying content in a specific way.