Facebook is the only universal method that works between iOS, Android, and even tablets.
If you want, I can:
If you delete the app without linking an account, or if your phone breaks, the local data is gone forever. Rovio (the developer) does not store progress anonymously—you must manually link your game to a cloud service. angry birds 2 save data
Don't wait for disaster. Perform these checks monthly. Facebook is the only universal method that works