What is the MPX200's discrete cable bag used for?

The quick answer is cable storage and retraction.

Cables running from the MPX200 hub beneath the table and through tabletop controller retract when not in use. The discrete cable bag that comes with the MPX200 protects these hanging cables from being snagged and keeps them out of sight. The bag also helps prevent the cables from getting tangled.

The optimized cable weights included with the bag smoothly guide cables back into resting position when not in use. They are also light enough to prevent pulling on the cables when connected to devices. 

The image below depicts the bag as transparent in order to show the weights and the cable extended for connecting to a device as well as retracted for stowage while not in use.