theshillito

The main use case for this seems to be when making an Apple Pay payment in-app or through Safari it shows the current balance of the account or card (and it refreshes the balance upon the Apple Pay interface opening). This is useful when making a purchase as it reminds you of your current balance so you're less likely to overspend. Sure you can open your bank/card app, but I expect most people don't do that before every online purchase. I'd say it's quite handy actually.

With Nanoakron's point regarding tap-and-pay, this likely wasn't implemented so your bank balance isn't shown to the retailer in the shop. Perhaps the notifications from Wallet for Apple Pay transactions could get a "Your balance is now X" tacked to the end of it. Monzo used to do this when they were a prepay debit card rather than a proper bank account since it would prompt you to top up the account, but not any more.

It does seem like early days for whatever this feature will grow to be, but it's worth mentioning that non-Apple Pay transactions and transfers appear in Wallet after you've connected, not just the balances, and for the past few years too. As someone who has developed something that uses the UK Open Banking APIs in the past, I know that the initial connection gives the app a full history of transactions up to the individual bank's limitations (usually a few years) and then any further requests are only of the past few months (or less if specified). So depending on your bank you may have a varying number of years of transaction history.