Board socks for surfboards are useful because they provide an additional layer of protection. They protect the board from scratches, dents and UV rays that can damage the material over time. They also make transporting the surfboard easier as they protect it from impacts and damage during transport.
Board socks are lightweight and easy to put on, reducing the hassle of packing and unpacking your surfboard. Finally, they also allow for easier storage as the board can be safely stored in the sock without requiring additional space. Of course, it's particularly practical if you just want to quickly put the board in the car, because with a board sock you ensure that the wax, sand and water stay in the sock and don't stick to the seats in the car.