What is the benefit of the 2nd stage? Why not up the 1st stage?

 

Spray a small shot out of the hole, and hit it with the second stage when you have traction.

 

One reason people 2 stage is to reduce cylinder pressure at low RPMs.
I.E....cust. wants to spray 250 total....1st stage is 150hp, activated @ 3000rpm, 2nd stage comes in @ 4500rpm. This will keep the car on the 250 total shot through the rest of the run as long as your shift extension keeps you above 4500.....mine keeps me above 5K.

Another option is running a single stage on a progressive controller. This gives you total control over the application of power. It will let you delay system activation and ramp the nitrous. I use a progressive on my 94 and it lets me make adjustments for track conditions. I can control delay and ramp times in .1 sec increments, and have my start % as low as 35%.

The cons:
On a 2 stage is each stage is all or nothing, the only control is when to bring in the 2nd stage.
A progressive is harder on the solenoids as they are being switched on/off (pulsed) very quickly. Our solenoids are designed with components built to handle the extra stress of being pulsed. Some of the older kits and kits using the smaller solenoids are susceptible to coil damgage from progressive controllers.

Either way you go to get the best ET you are going to want to be at full nitrous power as soon into the run as traction will let you.