title: Git: Why is a merge-base necessary
body: <p>I know Git doesn't save diffs in the repository (as SVN does). Instead it saves a new tree-object for each commit and new blob-objects for every file that has changed.
  So, when merging two branches, why is it not enough to merge only both branch-heads?
  Why must a merge-base be found to apply all the intermediate steps within a merge?</p>
  
  <p>Thx very much for each answer.</p>