What is the difference between types of vacuum seal bags?

Embossed vacuum seal bags have small air channels that allow the suction-type vacuum sealer to draw air out of the bag from the lower bag without collapsing on itself and trapping air. These vacuum sealers (like the Vac 'n Seal Elite pictured below) have the bag on the outside of the machine, and the open end is placed over a slot that creates the vacuum. They look like this kind of machine. So, the embossed pattern is necessary for the bags to vacuum properly. 

Flat vacuum seal bags, on the other hand, are used inside a chamber vacuum sealer. These vacuum sealers vacuum the complete chamber, including the bag and contents inside, so no embossed air channels are needed to suck the air from the lower portion of the bag. These machines typically look like the OP10 chamber vacuum sealer below.