Debris are used to research. Research can let you bypass lvl.1 items/ships and directly produce high level items/ships which can save time and upgrade cost. Of cause, the required production cost increase with the level of the item you want to produce. But some people refine all that debris instead of research, because like in the real world, research is too costly.
This is often considered to be a legion thing, since legion can afford this and let all its members benefit by set up bounties and exchange.