Existing favourites will be lost, but you can add them back via TuneIn. Once you add the stations to the database, you'll be able to browse them offline. The benefit is that you might only need 100 stations in the database, which will result in better performance than having 30,000 stations, where 29,900 are never even used. There is also a better chance that the stations will be up to date when you add them, and you can always update them using TuneIn if they ever stop working.