If your talking about the skill that elven warriors get, yes I found it to be useful. Especially when I'm in a group.
Sometimes when I'm in a small group and I get agro and am about to die. I can use the charm skill to reduce some of my agro and it will start pounding on someone else, allowing me to heal up a bit before taking the agro again. Charm has saved my life more than once.
No, Charm doesn't work that way. All it does is reduce your aggro , so unless the other guy has aggro on it as well nothing will happen.
In my groups I made it clear for the healers not to heal me as I had my own healing ability. All the times I used Charm the mob went to the second damage dealer. Not that I was ever the top damage dealer anyway being an elven warrior. :)