If you allow websites to check if Apple Pay is set up, one of two things can happen:
If you have a card set up in Apple Pay: Websites might default your shopping cart to Apple Pay and you might see the Apple Pay button on product detail webpages (it’s up to the website).
If you don’t have a card set up in Apple Pay: Websites probably won’t default your shopping cart to Apple Pay and you probably won’t see the Apple Pay button on product detail webpages (because the website can see that you haven’t set up a card).
Allow privacy-preserving measurement of ad effectiveness
Let advertisers measure how they’re doing without associating ad activity with you.
Block all cookies
Prevent any websites, third parties, or advertisers from storing Use the developer tools in the Develop menu in Safari on Mac