Your backup file is the most secure way to store the private keys from your Guarda wallet. It’s safely encrypted and very convenient.
However, it’s not a bad idea to save the keys to your most-used currencies separately. You would, for example, be able to export them to a new Guarda wallet, or another service. Just make sure that you store them somewhere highly secure - anybody who gains access to a private key gains full control of the wallet it’s attached to.