from what i have read, the only positive thing i could find was this:
-----Prolactin stimulates proliferation of oligodendrocyte precursor cells. These cells differentiate into oligodendrocytes, the cells responsible for the formation of myelin coatings on axons in the central nervous system.
other than that its all negative:
-----Elevated prolactin secretion can suppress the secretion of FSH and GnRH, leading to hypogonadism, and sometimes causing erectile dysfunction in men.
-----Prolactin counteracts the effect of dopamine, which is responsible for sexual arousal.
-----High prolactin is suspected to be responsible for impotence and loss of libido (hyperprolactinemia).