Burgundy

The area of Burgundy is essential for both Germany and France in almost every stage of the game. Bordering two French (Marseille, Paris), one German (Munich) and one neutral (Belgium) supply center one can immediately understand its importance.

The French side

If France does not trust anything, it could always occupy Burgundy in Spring 1901. Simply move one army there, and let the other army support this move. Germany only has one unit bordering Burgundy, so you can always make it. My advice would be to move A (Par) to Burgundy, and let your army in Marseille handle the support. In the fall, you could always use your army in Marseille to seize Spain, while an army in Paris is pretty much useless in the fall.

Another possible anti-German opening is occupying both Burgundy and Picardy in Spring 1901. This gives you a shot at Belgium while at the same time threatening Munich.

I believe a bounce in Burgundy could be beneficial for France as well. It protects its most vulnerable point, and if the bounce is executed with your army in Marseille, you still have the option to capture  Spain.

The German side

An opening from Germany into Burgundy will be considered very anti French. Unless you have arranged a bounce with France, a German army in Burgundy is simply an act of war. There are many openings where Germany decides to move to Burgundy, but not all of them end in a quick French defeat. Either English support is missing, or the army in Burgundy gets isolated, or Germany decided to take Belgium in fall 1901, which gives him no tactical advantage and leaves a very pissed and distrustful French player behind.

My advice to Germany would be in 9/10 games to either bounce, or just leave Burgundy a DMZ. Both France and Germany have plenty of neutral supply centers to capture. If played correctly, and respected by both sides, a DMZ in Burgundy could  be the start of a successful French/German alliance.