Waste Aversion

Capped inventory forces you to destroy items or upgrade inventory. Also, having small amounts of left over premium currency.

People to do not like wasting money, time or effort. Games are sometimes designed to force you to waste these things unless you pay to prevent it from happening.

One way that games do this is with a capped inventory system. If you are only able to hold 20 items and you collect another item, you are forced to discard or destroy the extra item. Games that do this will usually give you the option to pay to increase your inventory cap, and thus allow you to collect more items before your inventory is full again. By making it difficult or annoying to manage your inventory, games incentivize players to upgrade their inventory cap to push off this inconvenient task into the future.

When premium currency can be purchased in different amounts than what you can spend, you will always have some small amount left over. For example, if you can purchase gems in multiples of 1000 but only spend them in multiples of 80, you will have 40 gems left over at the end. Abandoning the game with unspent premium currency feels like wasting money, so players keep playing and keep purchasing more premium currency with the hopes of getting down to zero eventually and having nothing wasted.


Examples

AFK Arena AFK Arena
"Although it never has felt like there was a need to increase the inventory size at any point in this game."

World of Tanks Blitz MMO World of Tanks Blitz MMO
"You have a limited garage but can expand it by paying money or buying premium tanks. Not a big problem thought as selling old unused tanks has often benefits."

Walking Dead: Road to Survival Walking Dead: Road to Survival
"You can only carry so many characters. To carry more you have to pay."

Hay Day Hay Day
"Yes, but it can be raised by playing legitimately"

Harry Potter: Wizards Unite Harry Potter: Wizards Unite
"You can only hold a certain amount of potions, ingredients and energy. You have to spend gold to increase the limits."

Star Wars™: Galaxy of Heroes Star Wars™: Galaxy of Heroes
"Its nearly impossible to get down to zero crystals."