Good question... a lot of people have different opinions.
Tires are basically layers of rubber, steel and textile with some chemicals embedded to protect the rubber and make it last. Years ago,the tire mold was steel and it was coated with mold release or release lubricant...lots of it. Now, the molds are teflon composites (and other base materials) and don't require as much of it. There are some chemicals in the tire to protect the tire from ozone which causes the tire to deteriorate... that break down process begins when it comes out of the mold (see old thread about buying old tires.)
Some of the lubricant stays on the surface of your tires, reducing traction until it is worn away. If you buy a new tire and mount it on a rainy day, look at your tracks when you roll out of a tire store. You can see the release chemicals on the surface of the water. Some say that "Five hundred miles of easy acceleration, cornering and braking will allow the mold release lubricant to wear off, allowing the other tire components to begin working together." Others will tell you that scuffing them in a figure eight will wear it off quickly. Tire engineers I have spoken with told me that it has more to do with the heat cycle. When the tire heats up, the rubber softens and the chemicals come out to the surface....centrifugal force helps push them out and the asphalt wipes it off.... not really abrades it off...wipes.
Three or four heat cycles (15 to 20 miles at least 50 to 70 mph) will do it. Funny enough wagging your car back and forth does not heat up the tires.
Sound crazy? "What about those Indy and F1 cars I see doing it?" Well, that's on a different kind of tire. Our street radials need acceleration and braking to get hot. Those forces impart far more flex to the tire carcass, which is what generates the heat that then transfers to the tread compound as well. The F1 car tire is made to operate on a vertical plane for maximum traction at all times. Forcing those sidewalls to flex by violent back and forth DOES generate heat in their tires. Our street radials have side walls that allow the tire to flex back and forth. Working them front to back (throttle and brake) heats them up faster.
That said, I zig zag my tires on the way to the line...not to heat them up, but to get larger gravel off the tires to get them a little more traction on launch. For bigger hillclimb events, I will get a friend to run a glove over the tires to knock off any gravel stuck on the tire at the start line.
One other note on that... if you autocross a car with shaved tires, you will be amazed at the grip. Part of that is the fresh rubber exposed but ALSO it is partially more contact patch. Tires with low tread depth tires have more traction that tall new tread.There's a little more tread squirm until they wear down. New tire have less grip than you are used to partially because of taller tread. It takes some time to get adjusted to new tires...ask IRL driver Ryan Briscoe last night in Japan!!!
He was leading the series in points and leading the race last night, pulls in to the pit under green just as a crash occurs and yellow flag comes out. PERFECT timing. Everyone else has to pit under green. He hussles through the pit stop to come out in front of the leader which will gain him thirty seconds...and almost certainly give him the win. As he pulls out of the pit, he stomps on the throttle, new (pre-heated) tires spin and car spins... directly into the pit wall damaging his suspension and putting him at the back of the pack 8 laps down after repairs. HE COULD have cinched the championship last night. You have got to see that video. Wow.
One other note for AX - If you adjust your HOT tire pressures and are happy with the results, wait for the tires to cool down at the end of the day then measure the COLD pressures that resulted from your adjustments. That way, you'll know what cold pressures to use next time in order to achieve the hot pressures you liked.
Hope that helps a bit. I'm sure other will have other opinions differing from what I said here. Listen to all, experiment and form your own opinion of what works for you. You will not damage your car or street tires if you autocross on new tires... unless you extremely OVER inflate (like 42 to 55 lbs.) which will spin you .. or severely under inflate (like running 14 to 8 pounds) ...that will cause excessive wear and could de-bead the tire from the rim. Plus 10 or minus 10 off normal tire pressure is safe. If you are not sure what tire pressure to run..ask a more experienced driver like Zach or before the event, check on your car forums of guys with like cars and listen to consensus as a starting point.