Over time, these debris accumulate and can build up in hard-to-clean corners of your holding tanks, or on the tank sensors themselves. Once the debris comes in contact with your tank monitoring system, it can harden onto the components and not drain with the rest of the waste when you go to empty your tanks at a dump station.
This falsely indicates to the sensors that the tanks are more full than they actually are. People encountering this often complain that their tanks always read full, no matter how often they dump them.