While some cards are worth nothing, there are some extremely rare and extremely valuable cards
The first card checked has a[Security] effect, which trashes the top card of my attacking Digimon, turning it into a Digimon without [Free] in its traits or [Imperialdramon] in its name
When you can cost-reduce this down to one mana, why wouldnt you play it here
As an example, here is John Rolf build from the MPL: Creatures (27) 3 Knight of the Ebon Legion 4 Foulmire Knight 4 Smitten Swordmaster 4 Order of Midnight 4 Lovestruck Beast 4 Murderous Rider 4 Edgewall Innkeeper Planeswalkers (1) Lands (23) Spells (9) Sideboard This is the grindiest of builds, as it runs the card advantage from both the Innkeeper and the Clover
However, an Aura spell that doesn't resolveperhaps because its target becomes illegal in responsewon't enter the battlefield, and it won't cause constellation abilities to trigger