[Chris1529]

If you do your burnout and there is a very lengthy delay before you stage ( or when you stage), the contact patch of the tire tends to pick up the tracks rubber where the car was sitting. If I judge the delay to be too long, I usually try to do another burnout.
If the temp of the car is too high though, I won't do the second burnout.

I am in agreement that shorter burnouts to clean the tires are all that is necessary unless the track temp is really low.