One that I could think of is that it is a Axis port in SZ 110 and SZ 105. A few ideas that popped into my head that didnt work:
1. IPC’s (S. France is worth more)
2. Facilities (S. France has both)
If I take S. France, Italy is taking Normandy on I2 to bolster their Income. Straffing Normandy is also an option so that you can leave it French so the US cant use the IC there.