I can't think of anything in particular I'd want to erase. I've experienced the most pain over what hasn't happened in my life, rather than what has. (Maybe someday someone will figure out a way to implant fake memories....)
Also, I was thinking along the same lines as those who were mentioning there could still be some effect of what happened on behaviour, emotions and reactions, even if the explicit memory has been erased. There was a story in a neuroscience class I took about a woman who had brain damage in a specific area involved in forming memories. She retained the memories she had before the damage, but couldn't form new ones. Every time she saw her doctor, he had to re-introduce himself. Once when she shook his hand, he pricked her with a pin. She didn't remember the incident, but from that day forward she would balk at shaking his hand, and wouldn't be able to say why.
I can see this being used if the explicit memory itself is causing a lot of distress: frightening flashbacks, body memories, reliving the experience. In that case it could be helpful, even if it doesn't wipe the slate entirely clean.