AdNabu automatically finds and creates long tail keywords from the keywords provided by you. For eg: if a user gives the keyword attorney, AdNabu will create the following keywords (and more!) automatically and segregate them into single keyword ad groups.
When you use a single keyword attorney, you are already advertising for the search terms added by AdNabu automatically. But bidding for all these searches from a single keyword is not at all ideal. This is the reason why AdNabu creates ad groups and keywords for the long tail automatically.