The practice has now been abandoned by modern-style medicine for all except a few very specific medical conditions. It is conceivable that historically, in the absence of other treatments for hypertension, bloodletting sometimes had a beneficial effect in temporarily reducing blood pressure by reducing blood volume.

Did bloodletting actually work?

Did bloodletting ever work? If by “work” you mean ending a disease process, then yes. Most of the people who died after bloodletting perished from diseases that were incurable in their time period — but bloodletting probably didn't help.

What was bleeding and purging?

Cupping, bleeding and purging were common methods used to restore the balance between the humours. In the early modern era, illnesses were thought to be caused by disturbances of the body, which, when perfectly healthy, was held to be in an inner state of harmonious balance, like the world or the cosmos.