It can cut both ways. If someone's incompetent, it fails specatcularly — odds are, you create a monster. Halfway competent? You might manage to have the recipient survive to live some abbrrviated life. I suspect that's what happened to the Emperor.

[ It stands to reason, from what bits of information he can glean. ]

The very few who know what they're doing? They can save a life, but it shortens their own. That special blood had to come from somewhere.