If the harasser could get carried away in an argument and start beating, but didn't leave the house planning to kill, then restraining orders can limit the time the harasser is around you and limit the time before they 'blow their cool'. When the harasser breaks the restraining order and comes near you "just to talk, I promise", you can get the police involved straight away, and the harasser can be hauled off before they lose their cool, and things escalate.
A full restraining order is different.
This person knows where you live, where you work, who all your friends are, your family.
Yeah, right. You are expected to quit your job, take your kids out of school (who are possibly also his kids), move hundreds of miles away, and possibly still not get away because they are following you around. On a whim. Oh, and never contact your friends and family again, they can be watching.
Not an option for some people. You need savings and cash while hiding. What if you have children, can you just pull them out of school (say), while you hide? How long would you hide for? 5 years?