I used to Mod other RP sites before DE, and one thing that I learned from those sites is that when the membership is free to create RP threads when ever they want, and with what ever plot they want it doesn't turn out well for the site as a whole. I mean no offense to the membership by this, in fact I intend to do the opposite.
Experience has taught me that allowing unrestricted creation of RPs pushes the creative talents of the membership out and spreads it thin. When RP plots are completely unregulated the membership has a tendency to create and join more RPs then is healthy for the site.
Generally this would actually be a good thing, the membership would create and participate in a lot of RPs, building activity in the site. But here inlays the problem, the positive effects of the open system are only short term. The membership under such system spread their creative talents out over a great number of RPs in a relatively short period of time, this causes the membership to burn themselves out rather quickly and causes later threads to fall under lesser creative worth as the membership begins to run out of ideas and creativity.
We did start with an open system here on DE as I was hoping that the exceptional membership that we have here wouldn't fall under the same problem as other sites. But over time I began seeing some of the precursor signs of the inevitable collapse of creativity. Even the best membership will fall eventually, since humanity is not perfect, and neither is creative stamina.
So, for the long term benefit and health of DE, before the inevitable collapse, I set up a system in which the membership is required to wait for their RP threads to be approved by a member of the staff. By placing such restrictions the staff is able to maintain a stable number of RPs open on the site and are able to better maintain solid, creative plots. I would rather have a less restrictive method for this, but I have yet to find another way that would actually work beyond theory.
I am aware that it can be a bit of a pain, and frustrating at times. It's actually not all that much fun for the staff either, believe it or not.
It requires the staff to put in a lot more work then they would otherwise. But I am keeping the long term health of the site in mind when maintaining this system. But utilizing this system, the great creativity of the DE membership that we have is able to flourish and grow over time, without choking itself out.
Work hard here on DE to not be too restrictive on RPs. Most plots eventually approved, though sometimes are required to be revised first. But we have a solid membership here, so the need for revision or complete unapproval is a rarity.
Edit: Just realized that I didn't answer a couple of your other questions.
No, it's not because you're a Newbie, or have anything to do with your character's approval status. Every member of DE, regardless of rank or how many characters they have that are approved, or not have to go through the same system.
Once you're character(s) have been approved you are free to create a RP plot in any RP board that you wish, and join in any Main RP or Private RP (pending invite from the creator) that you'd like. But if you create a new RP plot it will need to be approved by the staff before it can be viewed and used by the rest of the membership.
I hope that answers all of your questions.