If you're in a relationship and are both clean, STDs are not an issue. However when only the female takes the pill its efficiency isn't 100%, so there is still

If you're in a relationship and are both clean, STDs are not an issue. However when only the female takes the pill its efficiency isn't 100%, so there is still a tiny risk of pregnancy. Having the male take a pill or similar contraception will pretty much nullify that risk (both the female and male pill would have to fail in this case)