It would be a nice feature if discount codes could be redeemed via link in the same way that EasyCoupon does it for example. This would allow merchants to send mails already including a working link to get the customer shopping with their discount. For the customers, this would make the journey smoother because they don't need to back and forth to get some code and find the field to enter it and so on.

Plus, the customer is probably much more likely to actually complete the checkout if they see their shiny discount applied at all times right from the moment they visit the store.