One is what happens if the tank preset is really low? Like 15 psi?
First, assuming no multi-dome feature, Diaphragm gets extended/stretched more than necessary. I would expect this to reduce tank life.
You do get a bonus storage available if the power goes off and you immediately stop using water.
If multi-dome feature, the extra interior dome limits the diaphragm stretching, but when the diaphragm hits the multi-dome, the pressure will suddenly spike and turn off the pressure switch. So more cycling than usual.
Multi-dome is a Well-X-Trol (Amtrol) term. Goulds hydropro offers "steel inner shell" which appears to be the same as multi-dome.
And what happens if it’s high, like 50 psi?
The pump will cycle on the order of twice as often. Also, you will get a stutter in water pressure for the time it takes for the pump to get going.
Or over the cut off pressure, like 65?
It would be as if you had no pressure tank. Expect the pump to quickly cycle on-off-on-off....
One more item. The 2 PSI is the common recommendation for submersible pumps. Those are quick to deliver water. That could be reduced to maybe 1 psi in many cases, but the 2 psi gives a little buffer for the diaphragm to lose a bit of air to the water. The purpose of the 2 psi or whatever is to provide water until the pump can deliver.
A jet pump takes longer to get going. So a bigger differential is recommended to avoid the stutter.
If you have a low pressure cutoff pressure switch (with lever) it is important to not get a stutter, because the pressure switch sees that as a loss of water and locks you off.