As a general rule, NO. Sex complicates everything, espcecially work. You find that the sexual tension you can build with a model will result in much sexier pictures than the afterglow of sex. If you can make her feel sexy by "wanting" her and not "having" her, she will usually perform much better as a model.
Sex is risky. I've had sex with a model, and we got along fine after, and she was better as a model because she wanted to please me more. I've also had sex with a model where we blew ALL the tension, and after that we didn't have much left between us, and so the resulting content was shit.
Best solution is, if you're gonna fuck 'em, wait until they're not your model anymore.
