If you mean a Single Member LLC (that has not made an election to be taxed as a corporation), it changes nothing for your Federal Income taxes. So there would not be any tax-purpose of doing that.
Some states (such as California) impose an additional fee for LLCs (California has a minimum $800 fee).
Although a LLC could give some legal protection in case of a lawsuit, most people do not treat LLCs properly for that regard, so the legal protection is minimal or non-existant. A good insurance policy can give far better protection.
