A German desaster
Hello!
Maybe Bismarck was no genius when it comes to dealing with France, but he was not a megalomaniac idiot like the little Austrian.
Actually, Germany occupied half of France during the war and remained in a number of fortresses as occupiers until the war idemnity had been paid (something France did at an unforseen quick pace). As long as France refuses to make peace, you have the occupation going on. Also, on friendlier terms, if France is unwilling to pay, you can also prolong the Germans' stay.
A simple occupation of France "because the Germans want it" would have been desastrous for several reasons:
a) guerilla warfare
The Germans already had mounting problems with the so-called Franctireurs. Things wouldn't go better.
b) international prestige
Remember, Bismarck had managed to present the Franco-Prussian war as a defensive war. Napoleon III had been trapped, sure, but he lost his nerve and declared war.
If Germany occupied/annexed parts of France on a Napoleonic (I) scale, it would have seen as an inappropriate grab for hegemony in Europe.
c) continuation of the war
France would not make peace. Germany would have to occupy it all and that would at that time mean a complete overstretching of its ressources. Prussia had an impressive military machine, but as in the 1940s, they were happier with Blitzkrieg. Remember, Germany in 1870 still lacked a lot of the industrial and demographic power it had at its hands in 1914 or 1939.
d) intervention
The longer the war already went and the unexpected results it had (crushing defeat of Napoleon III, coronation in Versailles, annexation of Alsace-Lorraine), the more antagonised Britain got. Under the circumstances you propose, it might as well have rallied allies to fight for the balance of power. Prussia already had some potential enemies, notably Austria-Hungary and Denmark. However, it would need the British a lot of money and diplomacy to convince them of another go. I cannot see Russia attacking Prussia in the 1870s, though. Maybe, though, a well-prepared British intervention would have been problematic enough.