By turning this feature on, you can automatically back up your wallet using your Gmail or Apple ID.
The fact that this is automatic means that even if you suddenly lose your iOS wallet, or forget your 12 word mnemonic, you can still restore your wallet. This is the advantage.
On the other hand, if your Gmail account is hacked or seized, it means that someone external can restore your iOS wallet. This is the disadvantage.
In other words, while there are benefits, it also presents potential risks.
Also, recently, there seem to be some issues with this feature. Even if you sync it with Gmail, the message “Sync paused. Enabling cloud backup to avoid losing access to your funds” appears quite frequently, and you have to re-login to restart the sync.
Considering these advantages and disadvantages, it would be best for only those who want to use it to do so.