Well. Kindred and sex - seems like a finished discussion in some ways. After all, Kindred don't have a sexual drive according to White Wolf and have the Kiss to take over its place. Not to forget having to burn blood to actually undertake the exercise.

Seems simple and straightforward. But it's not the end of the debate, just a start. Sex does have its uses, and hopefully we'll outline some of them here.

Control
Sex is a very powerful tool for control. Females have known this for many years, so have a few men. Sex, the intimacy of it (or at least the illusion of intimacy) is sometimes a useful tool, and Vampires are the master manipulators. Clans such as the Toreador, the Tzimisce, the Ravnos, the Ventrue, even the Brujah might concievably use this as a method of gaining some form of control over individuals.

Domination
Vampires have an urge to be in control, to dominate the area around them. Especially those who have, by virtue of nature or fate been forced into positions of power, the need to dominate their surroundings and others might conceivably become part of their personality. Sometimes, the safety of the blood bond on ghouls, the minor nature of mortals, or even other Kindred in the province of certain types of sex is enough of a satiation for these other urges. After all, if the rest of your plans and the world around you is slowly coming apart, the simple ability to control another during this encounter might be enough to put you in a better frame of mind.

Sadism
Manipulation, control, hurting someone. Making love to them and then leaving them, just to watch their reactions, dropping (or adding) Obfuscate at the beginning/end/middle of the act to scare/hurt/amuse yourself... the other provinces of it. All possible avenues for the Kindred that is not that close to their human side anymore.

Humanity
Getting in touch with it. Let's be truthful, not all Kindred are that close to being predators. And the act of sexual intercourse is a very mortal, human act. It is the creation/procreation of the race, possibly the closest thing that a man/woman might have with one another (sorry about the romanticism, trying to make a point). A vampire who finds himself slowly dropping away from his humanity, who finds the Beast closer to closer to him might try to grasp at this event, this action. Just to perhaps keep hold of their humanity, to feel, to be what they were. Probably doomed to failure, but a Kindred who is falling so fast might try anything.

Not the end of course
I've offered a few possible reactions, actions. A few possible reasons for Kindred to take part in the act of sexual intercourse to play Devils Advocate. I'm not saying that your character should, I'm just saying that there are reasons to do so. In the end, it's the choice of the player, but I would suggest that care be undertaken in such an action in-character. Do this because your character would, not because you would.