Offroad I find 28-30 is a great all around tire pressure for washboard, bumps, some crawling, and some higher speeds.
24-25 for limited high speed days and better traction and bump absorption. You lose a little clearance though, so it depends on what is more important. I find it a little mushy for higher speed fire roads at this pressure. Nothing terrible, but not a preference.
15-24 for sand, mud, snow. If you are just doing deep sand or deep snow, lotsa guys will run lower than 15 no problem at all and also get much better performance. I haven't encountered those conditions as the 24 has taken me around snowy mountains (but not on top of deep powder where the 10 psi might be much better).
If I have a mix of dirt roads, pavement then 32-34 takes the edge off and is comfortable for cruising. Normally I'd run 37 for highway and 35 or 36 around town.
None of this is an exact science so just some targets to shoot for or for context.