So, when youre facing an enemy that likes to use different spell cards, this changes the game because they cant cast their spells in an instant during their turn
Rares are where you start seeing more powerful build-arounds, board wipes, pushed creatures, unusual enchantments, premium lands, and cards with effects that would be miserable if they appeared too often in Limited
They also provide a platform for sharing your deck with others, allowing you to receive feedback and suggestions from fellow players
Thats not to say reds affinities are limited to beatdown
Mirran Crusader You probably never want to run this guy mainboard, but out of the sideboard he's an extremely potent threat against Abzan, both on offense and defense