When someone is paying, the shop does nothing else.
You don't need to know what WooCommerce does behind the curtain. You need one rule enforced: nothing — not backups, not stock syncs, not emails — is allowed to slow down a customer who is trying to pay you.
Stores make more chores than any other kind of site.
Remember the chore list? A blog adds a few chores a day. A store adds chores constantly: every order wants a confirmation email, a receipt, a stock update, and often a message to your accounting or shipping tools. WooCommerce keeps its own extra chore list (it's called Action Scheduler — you'll see that name in places) and busy stores pile it high.
Now add the funny rule — chores run during somebody's page load — and ask: who is loading pages on a store? Shoppers. Some of them mid-checkout. The person most likely to be stuck behind the chores is the person holding a credit card.
Two protections, one screen.
Chores move to the back room — the same thing SwiftQueue does for every site. Shoppers' pages stop being the moment chores happen.
The checkout gets a do-not-disturb sign. This one is store-specific: while a customer is on the checkout or payment pages, SwiftQueue refuses to start any background work at all, and order processing runs after the customer already has their confirmation. Paying gets the site's full attention.
Checkout protection (a Pro feature) arrives switched on — this screen is where you'd see it working, not where you have to configure it. Below it, SwiftQueue watches WooCommerce's own chore list (Action Scheduler) and warns you when it's clogged with old finished jobs, which is the most common reason store admin screens get slow.
"Will my order emails be late now?"
No — the opposite. Your order emails were always chores; they were already waiting for the chore list to run. SwiftQueue runs that list promptly and on purpose instead of whenever a visitor happens by, so the usual result is that order emails go out sooner and more predictably. The confirmation your customer sees on screen was never a chore and doesn't change at all.
What this doesn't do.
It won't make your product pages render faster. If every page is slow all the time, look at your theme and hosting first — that was never the chores.
It won't fix a payment gateway that is itself slow. If the card company takes four seconds, the card company takes four seconds.
The checkout protection is a Pro feature. The free core still moves chores off shoppers' page loads — that alone helps a store. The do-not-disturb sign and the Action Scheduler tools are in Pro.