Most people use it as a way to keep troll players away from their truck, however, players use "Rec" "Ban" for practically everything in the game, whether written in the tag, names or in chat, others use it just to troll, taking advantage of the word to gain "benefit". An example.
A truck ended up braking suddenly to avoid a collision, the driver behind has reduced braking time but manages to stop, even so he types "Rec" in the chat, often he even enters his ID. As if the truck that stopped to avoid a collision was to blame for something. These are daily events, it happens more in Calais-Duisburg, the rest of the map is calmer, away from arguments . But you can use "Rec or Ban" to alert other players that you are recording that moment.