Capped inventory forces you to destroy items or upgrade inventory. Also, having small amounts of left over premium currency.
"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."
"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"
"You need coins to upgrade your inventory, which can be obtained in-game, but it gets harder and harder to get enough coins."
"Limited to upgrading one building at a time. Paying opens extra upgrading slot. Troop and hospital sizes locked behind building levels."
"500 item inventory limit for all items. Players constantly have to break down useless equipment or use food."