real leather is "tanned" to make it durable. Tannic acid is used to do this and that reacts with the silver, tarnishing it. The tarnish can be polished away and is much better than the wear that mechanical friction and sweat from your hands would cause.
The only possible issue would be the acoustic damping that may be caused. If one believes that weighted bottom caps and other tune up items make a big difference, maybe this does too!
