A lot of games have items and game currencies available for purchase in their game store. This is more common in free games where players can buy items such as costumes, weapons, or even level up. That's how free games actually make money. How often do you buy items or game currencies? I sometimes do it to get items that will add fun to my gaming activities.
Honestly, if it is a game I enjoy, I may purchase currency once or twice a month if I have the budget for it. I've previously bought in game items before to get a pressing item that would otherwise take too long to get.