Me: 165# plus 10# camelbak Tubed 26" Hardtail, Tubed 26" FS. I run both on 2.1 normal volume tires. The terrain I ride most often is laden with planted granite rock gardens, and roots typical to NH woodland.
I gave up on finding "the perfect number" for inflation. My pumps have always deviated from actual pressure when a digital gauge has checked the supposed inflation. (even digital gauges have a 1-2 pound +/- at the kind of pressure we run for MTB. When was the last time anyone had their digital gauge or floor pump calibrated?)
I want to avoid flats and preserve my rims - and so rely upon one test and one test only - I take my thumb and depress one side of the tread pattern and agresssively try to reach the rim. If I can, it is too little, if I can't quite touch, I leave it. It has been working great for three years after I gave up on gauge readings. I have had the fewest # of flats using this totally subjective method.
Overly high pressure bounces you around and especially up and down which is very inefficient. Most riders want to put their energy into the forward vector.
Too little and you flat and dent rims.
If you ride smooth trails, pressure can be run low, but on chunky gnar, it will need to be higher to avoid bashing rims/rolling beads/burping/flats.
If you tend to ride into or over edges of rocks and roots versus flowing lightly over them, again, you will get a different result with the same tire pressure.
So my suggestion is to try try try various pressures until you get what feels right for you, using a section of trail that contains the typical terrain you ride.
I suggest, if you are a device reliant person, using +/-5 lb increments and see what you like. There is no right or wrong on this, just make an effort to do try for what works for you.
There are rides where I run low pressure, just because my butt is tired and I will be riding with slower paced guys who ride smooth flat terrain. That also enables me to creep up grippy ledges at low speed which is how I will have to ride every ledge section, instead of blasting up and over at normal speed over edges and using higher pressure to protect rims and prevent snakebite flats.
There are so many variables I haven't mentioned(setup of fork and shock/clumsy days/wet slippery vs dry ripper conditions/amount of gnarly downhill versus uphill/dropping off features, etc.. You may be a newbie who rides bike paths - what is the "correct" pressure for that versus lowland mud bog riding? Oh, you're a highland mtb park flyer... Oh, you run 1000 gram 2.5 tires or 1.9 400 grammers?