Keeps you from driving. We hope.
That depends on a few factors that I will now list in an attempt to emotionally scar you for life.
Who gets to be on top?
Is this a straight relationship?
If the above is true, is the woman the 'man' in the relationship?
Do you have a driver's license and a death-wish?
Were you weened too early?
Were you weened too late?
Do you like deep throating shotguns yet?
....
I think that's enough.

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****ing hippies
Seconded.
How the **** is having sex going to solve global warming?
Your guess is as good as mine.