Backup data is the 「mnemonic」, 「private key」, and 「keystore + password」.
Please keep them safe and do not share them with third parties, as if they are leaked, the same address can be accessed from another person's device.
If you do not store backup data, you will not be able to restore the address and the crypto assets and NFTs stored at that address in the event that you reinstall PLT Wallet due to a device failure, etc.