Probes are a great way to monitor two different temperatures with the same sensor. For example you could monitor the core and ambient temperature, or the temperature of two separate pieces of equipment if the probe is long enough. They also allow you to install the sensor outside of the equipment and still monitor the internal temperature if the sensor is unable to communicate with the hub from inside the equipment, or the equipment is at risk of damaging the sensor.
The best way to connect a probe is to power off the sensor by removing a battery and plugging the probe into the jack. Make sure the probe is all the way, if the probe is not connected properly it will not be registered by the sensor, it will also cause temperature sensor inside the IntelliSensor sensor to read incorrectly as the probe and internal sensor are connected to conserve power.
Once the probe is connected, power on the sensor. If the yellow and blue light flash repeatedly, this means the probe is not inserted all the way. Repeat the step above to correctly install the probe.
When it comes to installing a probe inside temperature controlled equipment, always makes sure the cable is securely fastened out of the way so it cannot be accidentally unplugged by people re-stocking or removing stock from equipment.