The Chicago screw post binding mechanism (to use its proper name) tightly binds pages along the length of the spine. Holes are punched on the left side of your pages using a standard paper punch and the pages are then placed onto the posts. Screw's at either end of the posts ensure the pages stay in place and are tightly held together.
Pros : Professional presentation. Your work is bound tightly at the seam and therefore your pages turn like they would in a bound book. Unlike in a bound book, however they can be replaced or moved.
Cons : Can be fiddly changing pages. Not hugely time consuming but not as simple as a ring binder.