It's kind of an ambiguous question as framed. The article was more about the individual health benefits of "sexual" activity.
The philosophical explanation for sex in general is gathered from observation:
Only animals that reproduced have ancestors living today. Reproduction in the wild confers no real benefit to the parental individual. So reproduction is one of those accidents that perpetuate themselves. There is no more purpose in reproduction than there is in the sea-cloud-rain cycle. Water isn't seeking a purpose and neither is reproduction. But both have consequences.
Ha. I won't even try to fix that sentence. I hope you all know what I meant. :-)
Yes, but does that sell magazines? You see?