This is something which has always annoyed me a lot and also confused me from a UX standpoint. It stands out to me as an example of a very poor UX decision that I see constantly.
When I'm browsing an online store and get to the checkout, I usually see a 'Promo Code' field. As any normal shopper, I want to save money on my purchase so I Google for a promo code. All of the resulting sites are built with very similar UX - there's a long list of codes which may or may not work and the user must click on a coupon to reveal the code.
What doesn't make sense to me though is why these websites always automatically open the merchant's homepage in a new tab once the code has been clicked.
Surely 99% of people looking for a special offer are doing so because they are already at the checkout. Or am I mistaken, in that most users decide to shop just because there is a promo code available?
Is there another reason I'm missing which would explain why these sites all exhibit this annoying behavior?