In a kinda slow motion way, every time u give someone something on there B-day that they like they gain affection towards u, which can cause more friendship between both of u and bring u closer causing more events, etc So yeah u do benfit from giving some one stuff on there B-day/or any other day as long as its something they like

its like giving ppl a gift they like on a regular day, but their affection grows a teeny weeny bit more. plus they say somthing different too. if u give them their fav item on their bday that will make them go up quite bit more but they'll say the same thing
ex: give kai pineapple on his bday (or on any other day for that matter) he'll like it more than just getting eggs or somthing, which he still likes but not as much.

sorry if that was a little confusing im just blurting out a bunch of ideas b4 explaining them

wtf are you talking about!! yes..yes..yes..yes..yes...yes..

when you are trying to woo a girl/boy, only give them 1 gift a day. the other ones don't
increase their affection, it just raises their friendship