Occluded Eye sighting is a bit of a more advanced technique but one everyone should try/use. It's very useful for quick acquisition. I'd recommend reading up on how a red dot sight works first and then it might make more sense as to why occluded sighting works so well.
Also, scopes don't work like iron sights. The front lens is not equivalent to the front iron sight nor is the rear lens like a rear iron sight.
Various BB throwers