Desire - quite a good reason. In mature and intelligent women it occurs frequently and is not usually directed to a worthy object. And if there is no "aggravating" circumstances (for example, a husband who is waiting at home), there is nothing immoral, even in fleeting relationships not. On the contrary, they can be an excellent discharge.
Other parameters that can be guided by a woman - the prospect. He's smart, he found his place in life, it's interesting ... Why not? Most women can enjoy sex only if they get to relax. That is, if they trust the partner. Knowing this, they are well aware that they will have to get used to your partner before everything goes perfectly. And for these women consent in exchange for the prospect - a natural and reasonable choice.
Another reason - a long abstinence. No there is nothing useful. Neither from a psychological point of view, nor for hormonal levels. So go for sex is called a "health" - not a bad option. Only it should be a decent man who is respectful to his passion. Otherwise, you can get even more deeply traumatized.
Another reason to agree to sex - it's attraction. Attracted to a man like a magnet. His appearance is surprisingly pleasant, he mesmerizing tone of voice, and so on and so forth ... After the drive should either disappointment or love. But in this case, risk is worth it. Again, if the object of attraction is not devoid of conscience and decency. Sleep with a dishonorable man should not be under any circumstances. It turns out our own peril.
The most correct and a good reason to join the communication - this is love. Especially mutual. And most women experience the thrill of it in the beginning of a relationship with a beloved man. And then, who knows, maybe you will be together for life.