I'm not completely sure, but I think it's because you are new to the forum and forums staff don't want you to rate abuse. Once you get over 50 messages it should be fine.
Why do I have to wait again for a moderator approval?? It worked before, without that thing. It takes ages til my things public because this is kinda slow
Double posting is when you post multiple times on the same post without pressing the reply button. And, if you forget something, you could easily press "edit" edit it.
As for the moderator thing, it is only to make sure that you do not double post, or do anything unfair to bring your number of messages up. That will be removed once you get over 50 messages.
Btw, you are allowed to post on someone's forum post without pressing the reply button, but you can only do it once, or it would be considered double posting.
Comments on Profile Post by dankness