Check automatically if the items client selected in cart are part of buy 2 for x$ or % off or whatever discount, and apply the discount to the products automatically. right not clients need to use the promotion interface to get actual discount. if this function is already there, sorry i didn't find anywhere to do it. The funnels check if the product is part of the discount item then ask client if they want to get the discount with window popup and additional selection at cart window. It can be a bit annoying for customer sometimes.