Thread strictly about the health implications

If you're trying to get a baby, semen retention is a terrible idea. It results in greater sperm DNA fragmentation and reduced progressive motility and it's associated with lower pregnancy rates and live birth rates

And regarding prostate cancer, it's not certain, but it probably increases the risk in those with low to intermediate risk

Full info here (with references):
https://alexleaf.com/the-science-of-semen-retention/