Linking your game account with a Google Play/iTunes account or an email address will save your progress in the game. You can still log in on the same device without connecting your account to any of these options, but if your device breaks or is reset then you will lose your game progress.

 

In case that happens, you are more than welcome to contact support and we will see if there is a way to recover the farm. Please note, that this is not always possible.