None. The .38 case is 1/10" shorter than the .357. Otherwise the case dimensions are the same. You will have to clean the cylinders before you go back to .357 though. The shorter cartridge usually leaves a ring of lube gunk in the cylinders. No big deal. It comes right out when you clean the revolver. A .45 calibre bore brush will help a lot when cleaning the cylinders.
If you're reloading, loading .357 brass to .38 Special velocities makes this go away. 2.5 to 2.8 grains of Bullseye with a 148 grain WC has been the standard target load for .38 Special for eons.