If your fence is not properly grounded when it experiences an extra electrical surge, it can cause some big problems, such as:
It could trip breakers It could cause shocks Your fence could stop working It could cause permanent damage to your fence system
While you may not even notice whether or not your fence is grounded most of the time, your fence will be affected and damaged if there were any electrical surges.
By grounding your fence, you're preventing major damage from other electrical sources, namely lightning.
Even lightning strikes that occur a few miles away could send extra power surges into your fence's electrical current that could permanently damage the system.