There is quite a few actually.

You get next mission for every 5 levels
The higher your friendship level with a ninja the stronger that ninja is in combat.
The higher your total friendship level the more ninjas will come every day, the more all party stats you get, the more gifts you can buy.

I think he means with another character, not ninja... the only use i found for friendship is 5 more attemps in TIs.

Yep, I got around 12-13 highest friendship, yet still the same 5 extra attempt only, with no change in anything else as far as I can see.

The task commission thing gives slightly more coins for higher level friends. Not amazing, but something...

Also, when you water a friend's tree, their tree gain more growth if you are higher level friend, I think it's 1 higher for every 3-4 lv friend. Note this only count toward the daily reward growth thing and not the level up growth. Having a good number of friends who can give you at least 3 exp on watering is the only way to guarantee being able to harvest daily (which is lv 8 or something)

we are talking about home new update..

Pretty sure that's called BOND level, not FRIENDSHIP level.
Unfortunately, the context provided can apply to both, but unless the op made a mistake, not something we should assume on a regular basis.
So no, we are not talking about the new feature unless OP comes back and say we are.

You can convoy as well matters :)

Talking about friendship with other players from what I see its not much benefit and wish they included more