Give coupons ability to be buy 1 get 1 (free, 50% off, 25% off, whatever).
Very basic coupon function should be buy 1 get 1 free or 50% off or whatever. Incredible this is not already available.
This is available via extensions already.
Luke Cavanagh commented
This is definitely lacking in the woocommerce coupon system!
Buy "x" get "x" free...using a coupon code.