"Blood magic" generally just refers to magic which uses blood as a physical charge. There's not much on the subject of it because it's almost never considered a branch of magic in its own right.
As for whether or not it's "good or bad," it's neither. It's just a component which you can use if it suits your methods. Be advised that your own blood is going to be endlessly more effective at powering your magic than someone else's. Blood sacrifice is not nearly as effective if the blood is not shed willingly for the express purpose of its use in ritual, unless the person shedding it buys fully into the magical framework you're using.