I've found them useful for target shooting, but I would prefer a single stage trigger in airsoft.
When I've used a 2-stage I've pulled the first stage after lining up my shot, and then after I've pulled the first stage I check my sights again. If they're all good, I pull the second stage.
Since where on the topic of triggers and them changing pull weight, there is also Set Triggers. Most bench rifles and long range varmint rifles are fitted with them. After the action is cocked, you can either pull the trigger like normal, or give the trigger, pad, shoe, what ever (All depends on model) a forward push, and the trigger then resets to being only 1-4oz pull. Meaning if you blow on it hard enough it will literally go off.
But yes, near every firearm has some separate stage. Most noticeable ones are the WW2 bolt actions like the Lee-Enfield and Mauser's, when you pull them, there is a very noticeable slack point where the trigger almost just falls back to a easier 4-5lb pull.