To each their own, and terrain and tire choice has everything to do with it. But my impression is many I ride with pump their tires up too high.
On my 26" bike (2.4" Mutanoraptor/2.1" Traction Pro) I ride 30 psi front and 40 psi rear.
On my 29" bike (2.1" Nanoraptors) I ride 28 psi front and 38 psi rear.
FWIW, I weight 200 pounds.
This is a nice balance where I don't get killed on rocks but can maintain traction up most climbs.
It's important not to go too low or you'll be in danger of snake bites and bent rims.
An easy way to adjust it to start with 45 or 50 psi, but leave your valve caps of and your stems open. Every mile or so reach down a release a quick pfffttt of air. Pay attention to how the rear hooks up on climbs, and how the front tracks on the downhills. You'll know when you go to low because the bike will feel squishy and have some side-to-side "flex". Plug a tire guage in and read what pressures you ended up at. Continue to play with your pressures in small increments. Higher for tacky and smooth rolling trails. Lower for loose, steep and dry.