I believe it has actual physical positive effect on the hair. High end expensive salons in Europe use bull semen for hair application. And two of the all time best with floor length accomplishment (Anya and Leona) have endorsed it.

From a relationship standpoint, and assuming you have a hair fetish, what would be more exciting than having your splooge contribute to her length, thickness, and shine?

For those who prefer PIV sex, you can capture the load in a NON SPERMICIDE condom and apply it afterwards. Wrap her hair in clear wrap with some elastics to hold it, and let it work the magic overnite. Wash in the morning.

Because all this is perceived as weird and fetishy, it does not get the acceptance that it would compared to something like coconut oil or almond butter as a hair application.