Roller spacing may affect desired practice. If You have 7 goot spacing and they blow a roller, you are more likely to have them bump than if you have one roller and 3'6" Spacing.
If you have 3'6" spacing and 2 safety rollers it will have less effect on production. Perhaps none at all since the 2 safety rollers at 3'6" take up the same space as 1 roller at 7' . You can also have more optimal thru put since if the first available roller is missed by the roller up timing the next one takes only half as long to get there if the spacing is haved. Of course, with a 200' conveyor you have added 30 rollers which has a cost.
At the end of the day the system is not fool proof. The Fool is bigger than the proof.
Luv the line about cost of teaching customers not to step on the Brake, or Steer, or find neutral. The first flaw in this theory is that they are all teachable.