Taking redundant level measurements is an important precautionary tactic to prevent spills in the event of sensor failure. While we expect our sensors to last a long time, they will eventually fail – as will any sensor from any manufacturer.
Failure doesn’t necessarily mean the sensor is completely broken. It may be that the sensor needs recalibration, or that environmental factors have caused inaccurate readings. Each sensor is designed with features to avoid this, but having another sensor in place, preferably of another type/technology, can ensure that sensor failure does not lead to disaster.