It will tell you in advance what the campground voltage is. In parks which have marginal voltage, the closer your site is to the panel box, the higher voltage you'll have. Avoid sites which are at the far end of the electric park's installation. But a circuit analyzer should be plugged into the rustically first. It tells that current is on, and the polarity is correct.
Reverse polarity can damage certain equipment, such as VCRs, TVs and computers.
Where there is an imbalance in the electric load, this device will shut down the entire circuit. It can be reset simply by pushing in the reset button. This can cause some unwanted surprises where the RV is equipped with an inverter, and unknown to the RVer the inverter runs through an entire battery bank before the problem is discovered.