TL;DR can you confirm transactions that are coming into your wallet before the rest of the network? Within a minute after the payment is made, or maybe even a few seconds? Just to confirm that the funds will be eventually unlocked, and without having to wait for the network to agree? It could be necessary for time-sensitive situations.
Imagine a theoretical scenario:
Let's say a pizza shop wants to spread the use of Monero and they decide to add it as a payment option.
Monero transactions happen relatively quickly, This arbitrary website claims that the transaction is visible after a second after making the payment, first confirmation is after less than 4 minutes and the funds are unlocked after 30 minutes.
But it might turn out that hey, the transaction wasn't valid after all, and that the pizzeria doesn't get the money!
What should such theoritical pizzeria do? Gamble, and start preparing the order right away and risk losing funds? Or wait for it to be confirmed but make the customer wait for an unnecessary time? Can the pizzeria confirm this particular transaction on its own in order to decide whether to take the order or not, and then let the rest of the network confirm it later in order to unlock the funds?
I am not very knowledgeable about the technicalities of Monero payments, so this question might not make much sense, but I think neither would the theoretical pizzeria owner.
For a pizzeria the lost fund are small, but I can imagine that there might be an industry where the stakes are higher, so the question still stands.