Frequently. I rarely use the balance, but I frequently use the fader.

...and I frequently use the balence and rarely use the fader. I rarely (actually never) use the fader as I have a Miata and there are only two speakers. I often use the balence, because when I am in the car by myself I shift the balence to be centred on the driver's position, but when my wife is in the car with me I shift it back to the centre.