First, a legal separation does not end your marriage. You cannot remarry if you are legally separated but not divorced. A legal separation allows you to remain married but live separately until either you reconcile or file for divorce.
Second, fault plays a different role. In North Carolina, neither spouse needs to be held at fault for a couple to get divorced. To obtain a legal separation, however, the person who files must provide information establishing that his or her spouse was at fault. Third, you can file for a legal separation as soon as you want, whereas for a no-fault divorce the parties must have been physically separated for at least a year.