There is no benefit. Samsung steals all of your data and then sells it to 3rd parties. You have no control over what company sees your interim ation and you will never be told how it is used by Samsung. They are using you to make money and not give you anything else.
Samsung pay is very convenient to have but not all local bank (check your bank institution to verify the card being added) supports mobile wallet or Samsung pay.. Earns point depends on what level you reach(how many times you use it in any stores that accepts it) and become silver, gold, platinum user.. Points can be converted to get stuff from samsung shop(may vary by region)