Like others have said, find your sweet spot based on what you like and feel good with. Beyond that, I sometimes make adjustments specific for the type of trail. I also adjust for altitude when traveling, although likely not necessary (just in my head 🙂 ). I like my tires around 28 lbs for most of the trials I frequent. I come in at 165-170 loaded, 32 lb bike, 27.5×2.4 with tubes. But, I have found that different brands and models of tires have a different sweet spot for me. For me, I run WTB’s at the lower end (25-28), Maxxis at the higher end (35+), with Kenda’s in the middle (30-32). I feel like sidewall strength and stiffness drives pressure to some extent (stiffer sidewall = lower possible pressure). Just my unscientific opinion.