Part of that is recreational - from a purely reproductive perspective a number of human sex traits serve no purpose.
I disagree, they all are there for a reason, and Darwin would confirm that..
For example, human females have orgasms,
thats so they enjoy sex & have more babies, despite the 9 month and future effort that ensues as a result
human male penises are larger than needed,
I thought they were a perfect fit
humans have sex during pregnancy, menstruation etc.
thats just an unnecessary consequence of everything else being in working order, rather than proving something in its own right