For those who are unaware of what vampirism is, it is essentially the practice of feeding off of the energy of others. What one does with that energy is a matter of personal choice and one's needs.
Traditionally, one stricken with vampirism requires the energy to survive. The use of another's life force is a means of prolonging their own existence. Most folks don't work that way, but there's exceptions to any ruke.
Vampires can be born, made, or the traits can be adopted. Those are listed in order of respective rarity, with those who are born into it being the most rare.
Those who are born into it, either with some defect or simply some internal need to feed for the sake of internal growth, work differently than those who have been made or who've simply adopted the practice. Their bodies function differently, both on a physical and spiritual level. The energy they're required/programmed to siphon works as an internal mechanism that can automatically cause their bodies to heal more quickly, or can be funneled towards spirital or emotional growth. Its an automatic process that can be changed through will. Usually, those born into it become aware of their tendecies and can choose to modify them in a way that works for them.
Made vampires are usually turned into a sort of parasite through trauma. Sexual assualt, severe bodily harm, or emotional breakdowns can cause such a thing to occur. They are generally broken individuals who have immense difficulty getting by, so instead of functioning in a normal or healthy way, they intentionally or unintentionally cause harm to others as a means of illicting a negative response. The energy of that negative response is siphoned from and then used to make the offending party feel better for a short while. These folks are often literal drains on society, be it financially, emotionally, or spiritually. These guys are like the Westboro Baptist Church of the vampire world. They're basically trolls (no offense to the land spirit) who get off on being jerks.
My experiences with those sort of folks has been nothing other than unpleasant.
The third kind are those who make themselves into vamps. Most techniques for it involve willfully siphoning energy from other targets, as if it were some sort of predatory game. It can be used to help and heal others or hurt them, depending on the psychological needs and desires of the the vamp in question.
Moralizing aside, each of the three sorts can be harmful or helpful depending on their level of training, their skillsets, and the intentions they decide to adopt. Any of the above can learn to take the pain from others, for example, and then that energy can be transmuted such that it inspires healing and recuperation from whatever damage they've suffered from.
On the flip side, its possible to simply drain a target of their life force. Done long enough by someone with enough skill, one could potentially kill a target.
There are benefits and drawbacks to those who choose to utilize such practices. While the siphoned energy can be used for personal growth, healing, glamours, protections, and other forms of magic, there are quite a few risks. The biggest potential sources of trouble manifest in the form of spiritual diseases. If you were to choose to siphon from the wrong person, you could take on their illnesses - for example, working on a cancer patient could cause you to wind up getting cancer. The same could be said for STDs, chakra issues, emotional problems, spiritual damage, and so on and so forth.
Its an incredibly risky set of practices, especially if you don't know what you're doing. It highlights the need for self control, as most vamps who come to me for help do so because in the process of draining others they've hurt themselves. When things get to that point, they can't heal on their own.
That risk is the reason why I don't teach others how to use such techniques. The cost is frequently too high for them in the end.