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I usually see the competitive cars cooling their tires after every run...just wondering why. Is it beneficial to the tire to cool them off after every run? I usually see people cooling off R compounds and Azenis. But our run groups are pretty large and we sit on the grid for awhile between runs...

 
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Zzyzx will probably chime in and give you better answers than I can, but the top autocross tires have need to have high grip right off the bat, so they tend to heat quickly unlike a track tire which takes some time to build heat. If the tire overheats, it starts losing grip and gets "greasy". Kumho V710, Azenis, Hankooks like to be cooled to keep this from happening. Kuhmo MX likes lots of heat so no cooling required and great tire for dual driver car. My Hankooks were getting to 120+ on the sunny side of the car this past weekend so I was cooling them before the first run...
Chris

 
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Thats about it...^^

you'll also see some people trying to heat their tires up (or at least trying to keep them hot.)

 
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its all a matter of where the tire compound has the most grip, some like it hot, some like it cold. If you've got one of the stone cold sticky tires, then you need to cool em off, if you've got the hot ones, then put blankets over them. I never could get enough heat into MXs to autocross, but they were great for long track sessions. They seem to be the most tolerant of heat, the rest of them don';t seem to like it much.