It would change the balance of power in Europe and would completely alter history.
France became the dominant power in Western Europe because its kings achieved a relatively centralized state compared to other European powers.
A centralized German state would likely be the greatest power in Europe, or the second just behind France. It would include the Netherlands, half of Belgium, and most of what is now eastern France including Burgundy. If you include Northern Italy as well you have a dominant power.
Much of Medieval history becomes similar to the first century after Germany united in 1871 - European politics is dominated by the question of how does the rest of Europe contain German power?
I see two possibilities. One is that the rest of Europe is able to contain German ambitions which results in a similar political structure that we have today.
The other is that the Holy Roman Emperor becomes the true primus inter pares in Europe. The other European monarchies acknowledge the German king as a sort of suzerain, and Germany arbitrates disputes between the lesser powers of Europe. In many ways, the German kings succeed in creating a new Western Roman Empire and restores the ideal of a universal Christian state throughout Europe. This utterly changes European political, religious, and legal thought. If the Germans are able to stop France from centralziing, they might even expand the HRE border's to its Carolingian frontiers making the "King of France" no more important than the Duke of Burguny or Margrave of Austria.