I don't think it is good to steal positive energy from a person as I think it may effect the person mentally and emotionally. although I am fairly certain the effect of it and duration would depend on the amount of positive
energy taken from the person.
Now if you took negative energy you wpuld most likely make the person feel better. But then by taking that negative energy into yourself you would then become temporarily effected mentally and emotionally. Eg: You may suddenly start becoming depressed for no proper reason that you can explain.
Now if you took both positive and negative energy from a person and a lot of it at once; then I would then theorize that the person would then become temporarily emotionless.