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
The value of these magecraft creatures is inflated by the steady, easily-established chains of spells: start with a learn card, cast Introduction to Prophecy, then cast more learn spells, then Elemental Summoning Better yet, Prismari has the cream of the crop when it comes to learn spells
Standard Procedure Its just a card from Standard
Its in the past! Fabled is already shaping up to be a whole new world (which I know is a card that is also being rotated out, but forgive me, that pun was undeniable)
In part thats because theres only about thirty of them in all of Magic , but they are definitely an important (if small) cog in our engine