Interior leather,although coated (which all leathers are or they'd be destroyed simply by being exposed to air) are still porous and "breathe". A high quality leather conditioner will penetrate the leather on a microscopic level. The leather will "drink" up the conditioner,and what's left you simply wipe off with a towel. If you'll notice,you sweat on vinyl but on leather you don't (or not nearly as much). I've also read many times that vinyl protectants can damage the stitching on leather seats,etc.