I grok it. 
I’ve always been fond of “ken” myself.
The usefulness in empathy is in completely understanding the other person. It gives you experiential knowledge with their emotions. But it doesn’t mean you are feeling what they feel. That, I agree, would be dangerous. You are feeling a small bit of what they feel, which is enough for you to get an emotional understanding of their problem.
Sympathy is far more cerebral.
Sympathy is a feeling. Empathy is a social skill.