Many people find it disconcerting to hear their voice singing a different pitch than they're actually singing. I'm not talking about harmony, I'm talking about the exact note you are singing, only in tune. This is why people who use live autotune usually use it for the front house mix only, and have no autotune in their monitor. From what I've heard it is even harder to sing in tune if you aren't hearing what your voice is doing. If you are hearing the pitch corrected signal rather than the actual pitch your voice is producing, it is harder to tell what your voice is in fact doing.