Stores that sell consumables live on repeat orders, but customers forget, run out and buy from somewhere else. Subscriptions fix that for some buyers, but many people do not want to be locked in. WooCommerce has a reorder button deep inside My Account and nothing that reminds anyone at the right time.
This plugin sends one well timed email. You say how long a product lasts, and two 30 day bags get a reminder near day 57, not day 27. One click puts the same products, options and quantities back in the cart. No outside service, no monthly fee and no workflow to build.