I had my interview recently. I was extremely terrified, because I had overstayed my F1. After researching and reading on this forum, we decided to go without a lawyer. On the day of the interview, I was really questioning my decision, since I saw other couples waiting there with their lawyers.
But our interview was such a pleasant experience, that I think bringing a lawyer would have only made the IO ask more questions etc. . I may be wrong, but thats how we felt.
So if you dont have a messy case, like isezer mentioned, I wouldnt take a lawyer.
Good luck!