Imagine there is zero visibility and your electronic chart plotter suddenly quits.
There are a couple buoys, multiple exposed rocks and several fishing vessels ahead pulling pots.
How do you determine which is which?
Luckily you have a paper chart onboard that tells you there is a RACON buoy nearby.
The chart identifies the RACON buoy with a morse code and that is what is displayed on the radar screen.
Now you can identify which targets are rocks or other buoys by their distance and bearing from the RACON as shown on your radar and the paper chart.