Just a thought for the OP.
You mention your horse being unhappy when you do up noseband (I'm presuming a cavesson, maybe with a flash ?)
Have you had your horse's teeth checked recently because the action of tightening the noseband could push cheeks onto sharp teeth.
You could also be tightening the noseband too tightly - remember you should be able to comfortable fit 2 fingers between horse's face and noseband. I should maybe be more specific in that you should be able to fit the fingers on top of the nose on the boney part, for example, and not on the fleshy bit on the side as some people tend to think
As for the purpose, it depends on the noseband.
A cavesson can be used for decoration or for attaching standing martingale, the grakle can lessen how much a horse crosses it's jaw, the kineton can give you extra brakes by adding nose pressure ...
IMO alot of people use nosebands to mask problems instead of looking into the real cause (ie teeth, bit not adapted for horse, hand too heavy, etc)