Is fungicide neccessary?

Hey everyone, I am growing a single plant in my closet. Im three weeks into flowering. For the most part the temp is is the mid 80's. Gets a little high sometimes. I have schultz three in one fungicide, insecticide. It says its neem oil. I have never had problem with bugs or mold yet after a few grows in my old place. So my question is should I be using fungicide for preventitive measures or wait and not use it unless I have to? Any opinions?