If you want to use Enpass across multiple devices, you need to enable sync to keep the changes synchronized. We recommend using cloud sync as it automatically takes a backup of your data with the latest changes; thus lowering the risk of losing data.
Also, you don't need to worry about the safety of your database as using sync is safe. Your cloud always contains a copy of same encrypted data as on your device. We download the whole encrypted copy and then decrypt it locally on your device for the real sync operation and merge the changes. Afterward, we upload the encrypted data on the cloud.
In a nutshell, your cloud is only a storage medium and no security related operation (encryption or decryption) is actually performed there. All such operations are performed locally on your device.