Equal to the incubus in class, vastly superior in intelligence and power, the succubus utilizes sexual energy for a multitude of purposes. Legends tell of beautiful women appearing to men in their dreams and seducing them, slowly draining their health and sanity. In reality, the succubus is not usually known to kill her victims. Unlike her male counterpart, she does not seduce and kill for pleasure. By all reliable accounts, most succubae victims never realize that their partner was ever anything more than a remarkably beautiful woman for whom they held exceptionally strong feelings.
One could argue, however, that the intense heartbreaks suffered by those the succubus seduces and then leaves is far worse than the inescapable, withering death visited upon the victims of the incubus. But by all reliable accounts, a succubus is generally kind, gentle and affectionate. According to some stories, the succubus sometimes even chooses not to move on, but instead remains with her human lover throughout his (or her) lifetime.
Of course, she is still a demon. Although not necessarily evil, it would be unwise to cross one.
Additional: It is highly probable that a succubus and a human male can breed, but I’ve been able to find no evidence to suggest what sort of child may be produced by this union.