Items: You can combine items instantly. You don’t even have to put the last component on the hero - when you click on the item, the game sees that you have the needed components and you can upgrade with a click instantly. This is good not only in terms of convenience – upgrading instantly makes items more useful because you don’t have to wait a whole round for the upgrade, which could be crucial in the late game.
Upgrading heroes: if you have two heroes on the bench and a third one on the field, an “upgrade” button appears above the unit, which makes upgrading units a bit more convenient.