They serve to give your side of the board tempo by allowing your creatures to attack (removing defenders), giving you more time to set up the board (removing attackers/expensive creatures), and allow for combat tricks (saving your creatures after damage is on the stack
Set your sample directly as a card count, or specify it by turn with a play/draw toggle the starting player skips their first-turn draw (rule 103.8a), so you have seen one fewer card on the play than on the draw
There are also no negative secondary effects of this attack, meaning that trainers can use it over and over to break through almost any defense and lay waste to the opposing team with remarkable ease before they can even react.
Now winning through combat damage gives way to combo kills the further up the brackets you go, but I can see Cloud decks rocking well in Core and Modified Brackets
Effects and spells behave like normal on the stack
Utility & Defensive Energy: These cards provide a benefit in addition to providing Energy
