Capped inventory forces you to destroy items or upgrade inventory. Also, having small amounts of left over premium currency.
"You can only hold a certain amount of potions, ingredients and energy. You have to spend gold to increase the limits."
"Although it never has felt like there was a need to increase the inventory size at any point in this game."
"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."
"You can only carry so many characters. To carry more you have to pay."