Why is it best to leave fibroadenoma in my breast?

Tomorrow jun 3 I request to have a talk with my surgeon about my results from my biopsy,we did talk on the phone but is not enough. As everyone that as read my questions know,I have a fibroadenoma on my left breast,my plastic surgeon call me and gave me the good news on the phone from my biopsy,mammogram and ultrasound,is benign and he doesn't want to remove it,I'm not agreeing with him all the way,I'm scare..again we schedule surgery for breast augmentation on that phone call for JUN 4,IREALLY WANT TO KNOW WHY HE THINKS IS BEST TO LEAVE IT IN MY BREAST?? Lump is size of a marble