I live in Southern Nv, and I air down every time im out, which is just about every other weekend. I find that my tires last much longer since im not chunking the tread off on rocks. Rather, my tires are conforming better and gettign better forward bite all day long. Plus its much easier on the chassis parts too. I have a perfect example. My buddy never airs down. Th two of us are running the same tire and just about the same size. My tires are 10months older and look better than his. Its all preference. I like my tires to do their job. Now saying all that, Im running around 25psi for the same trails ol ronny boy there is running. I can run fast and hard safely with this pressure, or if it gets a little more rocky like one of rons pics,Im aired down enough that the tire is pretty compliant and grips well.
To each their own. All I can say is that I like airing down, and my friend doesnt. I usually make it up most hills slower and smoother with less wheel spin, while he has more tire spin and and his tires are more chewed up. Just my .02