What is the purpose of the "use" button when I tap a villager ?

When you tap a villager a menu appears. At the bottom you can see a "use" button in blue.

Click on it and if you have a birthday cake or a mushroom grog, for exemple, you can give to him. But what is the effect ?

The Mushroom grog gives 100 xp to the selected villager.

The Birthday cake changes some clothes for your villager.

The Love potion restores all the happiness to the selected villager.