Having an account binding allows you to restore your progress if you reinstall the game or change the device. 

To link your progress, you need to:
1. Open the Settings menu in the game.
2. Press Link the account to save game progress.
3. Choose to enter with My.Games, Apple or Google Play depending on the device you are using.
4. Follow the steps on your screen.

In case you did not link your account and lost your access to it, please contact the customer support through the "How to restore my lost game account?" article for further assistance.