Genjutsu maybe one of the most powerful fighting tools available in NV not because of how deadly it is but because of how it can be used. First of all to get out of a genjutsu you need to have higher chakra levels than the caster if its 1 on 1, if you don't you're screwed. If you do have higher chakra levels thing is now do you even know that you're in a genjutsu, and if you do get out you're now hesitating because you're not sure whats real or what isn't. What else is dangerous/useful is while you are in a genjutsu is what the caster is trying to accomplish whether its gathering information, manipulating you to do something you normally wouldn't or just killing while you distracted all of this can be accomplished through the use of genjutsu