[Hunter]

Originally Posted by Coder8

Hunter, knowing that your in a genjutsu IS VERY benefitul(sp).

Spoiler:

If shikimaru didnt know he was in a genjutsu he wouldnt have known to break his finger to escape it. Or do you think he would just random break it anyways

Actually in this case, it doesn't matter, he couldn't ignore it.

Spoiler:

re-read this part of the manga, it's impossible not to know that the weird universe wasn't a genjutsu lol

Now, we can imagine a Genjutsu which would seem perfectly like the real world, and which wouldn't paralyze the opponent.
In this case it could be useful to know that the character than you see aren't real (because they wouldn't have chakra system or something like that).