Both.

You need to fully understand your car and be able to push it to the limit (yeah yeah, song just came on). Tandem driving takes skill to understand how the other driver is reacting, same thing with circuit. You need to read what is happening in front of you.

Great drivers can handle both styles. Look at a circuit driver, they are capable of handling a car in a drift as they encounter the breaking point of their tires or the effect of giving too much gas too early.