Think of throat as being the "birth canal" of the barrel. What happens there, will have a huge influence on the path the bullet takes over it's short life. If a bullet hops, skips and jumps from the case to the bore, then there is a good chance that it will enter the bore, off center, with regards to it's natural axis. The bullet forms to the bore in this position as spins towards the muzzle. Once the bullet exits, it becomes conflicted between two different axes, the natural and the false. The two struggle all the way to the target. This certainly affects overall accuracy.
Some folks, in an effort to improve accuracy, will purposely seat their bullets out into the lands. A lot of them do so without really understanding the mechanics of the problem. Some folks fireform and neck size their stuff in an effort to improve accuracy without really understanding what it does. The mechanics behind that is to reduce the amount the case shifts when chambered, which can have a direct bearing on the alignment of the bullet with the bore.
For the most part, I machine the throats separately. The throat reamers I use are .0005 over bullet with a one and a half degree lead. This, along with a good set up, assures as straight a path as possible, for the bullet to travel from the case to the bore. It's amazing how much consistency is affected by the throat.
