Antistatic spray is used to prevent accumulation of the static electricity on the field tiles, robot wheels, and any other non-conductive surface.
During the winter months when HVAC heated air gets dry inside the buildings, static electricity can accumulate and ESD (electro static discharge) could damage sensitive electronics.
V5 brain and motors happen to be missing robust ESD protection and this resulted in a lot of damage last season:
V5 brain ports break continually
7 BLOWN PORTS IN LESS THAN A WEEK!?!? What a joke.
How Do You Fix Broken Ports For v5?
V5 Ports Keep Dying
V5 White Screen Call for Replay?
Broken V5 Smart Ports
… and more …
To avoid costly equipment damage VEX recommends using antistatic spray in their Knowledge Base article: https://help.vex.com/article/148-vrc-team-esd-notice
Getting large bottle of spray makes perfect sense if you have full field and/or hosting competitions.
For the small setups (like 8 foam tiles sitting in the basement) there are cheaper alternatives. For example, we use laundry dryer sheets that contain some antistatic to wipe our tiles and robot wheels every couple of weeks, once we start heating the house.