Always on lets you make purchases with your powered and unlocked phone even it's not open to Mobile Pay - Mobile Pay opens automatically and the transaction's done in just a second or two.
You have the option to turn the Always On feature on and off in your Mobile Pay settings menu. You can also set the default for Tap & Pay to Affinity Mobile from within the Tap & Pay settings menu on your device. If you don't set the default for Tap & Pay to Affinity, the Always On feature won’t work.
Affinity has also enabled a Pay Now shortcut from the Affinity mobile app login screen for your convenience. It takes you directly to Mobile Pay to complete a purchase.