Smooth zipper action.  These are great for keeping your cards stored together, but also in their top loaders for extra support.  You keep the card in better condition inside a top loader; it's nice to be able to have them all together in one place that is easy to transport and easy to carry.
 
4 Pocket holds 96 cards - perfect for an entire set of chase cards or vintage 65 card sets
9 Pocket holds 216 cards - great for an assortment of your better cards
 
If you are a vendor, you can use these to not only sell your single cards, but also package it as a set that includes the binder with purchase.  Customers will be more apt to purchase a collection if it's already in a binder.
If you are a collector, these are a great way to transport your cards in top loader form to and from shows.