From what I know, there are no restrictions on a newly registered member that are not the same as any other member on the board.
There are only a few Administrator only forums where no one can go but board admins.
However, if you ran into a "Summation Mode" thread, then yes, there are restrictions there for everyone.
When a thread gets really long, or otherwise happens to be ending for whatever reason, the admins can turn the thread into "Summation Mode." This is a mode intended for everyone involved in the discussion one last post before the thread is closed to everyone.
If you did not post at all in the thread before it went into Summation Mode - You are no longer allowed to post at all to this thread. This goes for all posters, not just new posters.
If you did post in the thread before it went into Summation Mode - You are allowed 1 more post to the thread, but that's it. After that one last post, you can't post anymore to the thread either. This, again, goes for all posters, not just new posters.