If the question is "How Can Managers Help Retain Technical Women?" - how is paternity leave relevant (unless the father in the relationship works for the same company, I guess)?

As a woman, I'm much more likely to take the amount of maternity leave I desire if I think there's no professional penalty for it. Ensuring that men can take leave lowers the chance I'll be penalized for my decision since it's now a 'cost of doing business' and not a 'cost of hiring women'.

If only women have legally mandated paid time off for new kids it'll provide even more reproduction-related disincentive to hire women, which is reason enough for it to be relevant, I'd say.

Exactly! I have anecdata from German managers """jokingly complaining""" about how one can't hire young men any more because of their potential paternity leave. This is a good thing.