If you do it early enough you can take Gibraltar without the need for a navy. It does open up more landing spots for the Allies but taking the base from them is a hindrance to the American player. And if you maintain parity with the Soviets above the Black Sea you can then undercut them through the Caucasus.
Unlikely to be worth it though. Opening up the weak points in both Spain and Gibraltar doesn’t help the Axis. And those 8 inf in Turkey are a real pain to take out.