Should i add funds for this purchase ?

I am on my way to buy my new iphone and earlier while i shopped i saw some instructions from apple that said the best wauy to purchase without an upgrade was to add funds to my ape cash or apple pay and then go for it. My first question is am i reading thos correctly? More importantlly though. am wondering if there is any benefit from this? Will it cost more for me to buy it straight from my bank account or will I gain anything special by using apple pay? Any help i can get would be greatly appreciated and highly valued