The problem is that in some threads, Double Posting makes sense. Like for character sheet listings by the GM for an RP, or that new Artist scenario, or of course the ask threads with lotsa pictures. Sure, in most sections of the forum it makes sense to not want to have double posting... but it's not like this forum has a point system, virtual money system, or anything that is gained by posting more.
I can't comment on the RP Character Sheets as I don't use the RP forums. But as for the artist scenario, you're allowed more than enough images per post. 15 to be exact... If you need more than that, you can always upload them to dropbox, or a public imgur album.
Well, I know that it's much easier to edit character sheets when they each have their own post, and as the GM for an RP system style role-play, it would be up to them to post the character sheets for the group game. I haven't done it here yet, since I've been fairly light on the amount of information being shared, but on another forum, I've had to separate each character into a different post for ease of edits and to quickly link people to their characters. Though, with the character sheet database, most threads are only really occupied by one pony, who could post many times with their own OCs or RP Characters. That, I think, would be the part of the forum most affected. Takes freedom from being able to make the multi-posts of characters, then linking people directly to one. I'm still not understanding the purpose behind dissuading ponies from making multi-posts in the first place. I understand it on Solia or Gaia, but Solia actually put a system in place where posts made in certain sub-forums don't count towards total posts for the month, (namely - RP and Games.) However, both of those forums have a money system and a graphical avatar building system with an auction house and etc, etc, etc.