What is the difference between a 3-sided and 4-sided table throw?

4-sided (closed back): covers the whole table top with a 30" drape on all four sides. It hides everything under the table, which is nice when the back of your booth faces the crowd.

3-sided (open back): 30" drape on the front, left and right, and only an 8" drape at the back. You can sit behind the table and reach the storage underneath without lifting the cover.