Most people will tell you not to tune coilovers by adjusting the nitrogen pressure. Tune with valving and spring rates. Actually, I'm pretty sure King says the same thing. Technically they're right, but some adjustment to pressure can give you an idea where you want to go with valving and spring rates.
While going to school for my 1st degree at UNOH, we were taught as a rule of thumb to keep it to +/- 50psi on a given valve arrangement. So....if you started at 200psi (typical starting point) and were happier with things at 150psi, you should consider shimming for further adjustments.
The problem with too low of nitrogen pressure is the possibility of creating vacuum under the piston and/or having the oil foam up. When that happens you cavitate the shock and can damage it. Monitoring the shock temperature will give you a pretty good idea of what's happening inside the shock body. Before making any changes, record the current operating temperature of the shock body with an infrared thermometer. When things get unhappy as you make adjustments, you'll notice that with the IR. Higher pressures help with cavitation and will lower temperatures.
