[member="Jazzzz"]
It serves the same purpose as the Pre-Factory section in the Factory Discussion portion within the Factory itself - to allow a prospective submitter to work on their submission prior to formally submitting it to the Factory for review by a factory judge. This has been a common practice because there was not a designated, official, Pre-Factory section within the factory itself until recently. The practice of housing a pre-factory/codex area within a faction allows them to get input from other faction members, have a place on the forum to save their submission in stages (i.e; editing their post to add/remove content), and otherwise refine it so it is ready for a factory (or codex) judge to review.
More or less it is for work-in-progress stuff, things which are not yet ready to be submitted for approval or stuff which you want feedback on.