dalishious:

Some things blood magic can do:

• Repair lost eyesight (as mentioned by Sweeney in the Magi Origin) and other means of healing the sick* (as said in the Responsible Blood Magic codex entry)
• Restore failing crops*
• Create defensive barriers* or disrupt them (as done by Merrill in Long Way Home)
• Cleanse the Blight (as done by Merrill to her eluvian, and Isseya to the griffon eggs in Last Flight) and otherwise resist it (as done by Avernus)
• Determine if someone is possessed or not (as done by Merrill in Enemies Among Us)
• Track a missing person (as done by Gascard in All That Remains)
• Be used offensively or defensively like any other spell

Blood magic is no different than any other form of magic. Meaning it all depends on how someone chooses to use it. You can kill someone with blood magic just as you can kill someone with a fireball. But the Chantry doesn’t mind sending mages to throw those in their wars.

*This is said in the IDW Comic #3, so it’s debatable if canon or not.