If you don't encrypt your iPhone backup, the data stored on it may be vulnerable to unauthorized access or malicious attacks. Any personal information, such as app data, contact information, and photos, can be accessed without your permission. Additionally, if someone were to gain access to your device and its backup files without encryption enabled, they could potentially steal confidential information that could be used for nefarious purposes. Therefore it is important to enable encryption on any iPhone backups in order to keep your private data secure.