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

WWE Champions 2019 WWE Champions 2019
"Medals and belt slots"

HATSUNE MIKU: COLORFUL STAGE! HATSUNE MIKU: COLORFUL STAGE!
"There is no capped inventory system, however, the options to buy premium currency often mean you have a tiny bit left with nothing you can spend them on, unless you were to buy more premium currency."

Last Fortress Last Fortress
"While you can wait to increase levels/inventory level for free you fall behind if you do this. A need to pay to increase inventory level to advance in the game"

Gossip Harbor: Merge Game Gossip Harbor: Merge Game
"Storage can be increased with gem purchases"

Seaside Escape Seaside Escape
"Storage can be increasee by paying gems"

Merge Mansion - Mystery Game Merge Mansion - Mystery Game
"You need coins to upgrade your inventory, which can be obtained in-game, but it gets harder and harder to get enough coins."

Dream Hopper Dream Hopper
"wishes can be increased from 3 to 5"

War and Order War and Order
"Limited to upgrading one building at a time. Paying opens extra upgrading slot. Troop and hospital sizes locked behind building levels."

Tower of Fantasy Tower of Fantasy
"500 item inventory limit for all items. Players constantly have to break down useless equipment or use food."

IdleOn - Idle MMO IdleOn - Idle MMO
"Storage maximums"