My mum's horse is a roarer. It has never been an issue, so it was never operated on. I knew the horse as a 3 year old and he roared then, he's in his early teens now. His stamina is slightly affected, but not to the point where he can't be ridden, shown, etc.. He is fine in the arena, outside, in dusty environments, etc..
He is treated like a normal horse and other than sounding like a dragon and needing a bit more time to "cool out" after a workout he is normal.
I've known other roarers who have had the surgery and it's been 50/50 whether it worked or not.
So, I'd like to echo the advice of getting a vet to examine it, but in my experience fixing the roaring is more of a cosmetic thing, especially for a pleasure horse! The only problem is you can't sneak up to people while riding him :P