I have heard, read, etc that you want .75 twists per inch or you're sacrificing performance and noise. Personally, I have never noticed a difference. I usually shoot strings that I didn't ship to a customer because of it being too twisted, or not twisted enough. And I have not ever noticed anything.
Now, it is absoulutely no twist in the string, I'd say you need a new one, but I've had some that bad a twist ever 3" or so and it was fine.
On the opposite end, if a string is so twisted that it kinks up, i'd get a new one, but i do believe you could shoot it and be fine.
Sorry for not standing on either side of the fence, I've just never noticed much difference.