What is the point of getting the four happy items?

And by "the happy items", I mean the four items/foods that makeup the clover on the Tamagotchi 4U. What is the point of getting these four items? Do you need them all to do something? I don't get the point.

I know that other Tamagotchis (Like the Tamagotchi P's, except they have puzzle pieces instead of clover leaves) have the same kind of system. Do the four items do different things on different devices?

Thanks for your help in advance! ^_^

I have an iD L, and the things you're talking about are called Happy Stamps/Symbols. I'm sure the name is similar for the 4U. Basically, once you have all the stamps your character reaches Tamatomo level. Tamatomo means that character gets registered in the Notebook (again, pretty sure the Notebook is there in the 4U or is something similar), and more features and destinations get unlocked.

No destinations unlock on the 4u. When you obtain the Tamatomo for all 10 inbuilt characters you can receive an item/food from each character in the park. It will also register them in the notebook with a special screen (like the ID's).

With the download characters it just registers them in the notebook.

On the IDL series and P's different generations raised to Tamatomo unlock new

travel destinations and Icon backgrounds.

The aim of the P's is to get the blueprints to build a rocket and you get a blueprints piece with each of the inbuilt characters raised to Tamatomo.

Both also register characters in the notebook.

On the ID you get a balloon in your garden at 5th generation and a banner at the 11th. No notebook but the 11 characters show on your status screen when they've reached Tamatomo.