A recent study indicates that men who ejaculate every day have a lower risk of prostate cancer than men who do not ejaculate regularly.
Further reading: Giles, G.G., Severi, G., English, D.R., McCredie, M.R.E., Borland, R., Boyle, P. and Hopper, J.L. (2003), Sexual factors and prostate cancer. BJU International, 92: 211–216. doi: 10.1046/j.1464-410X.2003.04319.x