Whenever you make an online transaction with fiat, you expose your personal information to merchants and transaction processing companies. By using a Visa Giftcard, there is no way to link your identity to the transaction, unless of course you are shipping something to your house. Companies like coinbase and paypal require KYC which log all your transactions and send personal data to merchants, making it increasingly difficult to be anonymous online. The Visa Card works just like a debit card and can be used on most websites.
Since a card is only valued at $25, $50, $100: It’s only really good for a few transactions. Your mostly going to be wanting to use the cards for online services, or empty it, and use it to sign up for free trials. You can add these cards as a payment method on PayPal, but that kind of defeats the purpose of being anonymous, unless your PayPal isn’t linked to your personal identity in any way.
Selling crypto for cold hard cash is the main method of unlocking your value anonymously. However, that requires physical interaction, and you can’t use cash for online payments without depositing it somewhere that requires KYC. Visa Giftcards bypass this whole problem. It’s basically the most secure way to pay online without a leaving a trace.