The first and the foremost objective of having using a ground rod is present a designed electrical pathway to route a static discharge voltage to earth. This technology is used mainly to
protect any form of construction from lightning.
AC will seek a path to the AC source, DC will seek a path to the DC source and a Static Discharge (Lightning) will seek a path back to its source usually earth. If a return path is not designed for that return path or multiple return paths exist current will seek its own paths back to its voltage source.
When current seeks and find its own paths back to its voltage source usually it will pass through equipment. It the voltage passing through that equipment is higher then its operating threshold that equipment will fail and an outage of some type will take place.