I believe the sheath is just for looks - some people don't care for the teflon insulation look I guess.
![Smiley Smiley](https://www.decware.com/yabbfiles/Templates/Forum/default/smiley.gif)
Personally I prefer most of my speaker cables without termination, it's just that couple of percent better sounding to me. That said, I usually terminate with silver banana plugs because I'm often swapping out speakers and testing different amps, so I like being able to quickly swap stuff out. Otherwise, I just run the wire naked.