You may sacrifice zero lands as you cast Devastating Summons. If you do, you'll put two 0/0 creature tokens onto the battlefield as the spell resolves. Unless some effect (such as the one from Glorious Anthem) is boosting their toughness, they'll be put into the graveyard as a state-based action. Abilities that trigger when a creature enters will trigger, as will those that trigger when a creature leaves the battlefield.