These are used by platforms in order to improve passive scans. They sweep out the entire orbital quadrant for ISR flux.
This will only highlight anomalies, i.e. increase the chance of performing a scan. It does not in any way increase the chance of a successful scan as this is dependent on sensor power of the platform and sensor profile of the target.
Sensor nets are therefore used in conjunction with sensors.
In order to guarantee a scan, 25 sensor nets are required in orbital 5, 100 in orbital 10 and 225 in orbital 15.