Apple Pay settings

What is:

'Automatically select this card for Apple Pay when you make purchases where it is requested'

MacBook Pro 13 inches 2018 model

macOS 10.15.1

when I added a new card to my Apple Pay via my iPhone 8 Plus & made it the default card (I want it as the default card) it automatically selected 'automatic selection' does that mean it's the default card?

Should I do the same setting on my MacBook Pro as my iPhone?

Can only the default card have this option?

What's the difference between that setting & the default card? I'm confused.