Why does Retailmenot open a new tab when you clicked on a coupon? [on hold]

I have a question about promo code sites like Retailmenot.

When you click on the coupon button, it doesn't redirect you to the store page, but the thing they do is that they open a page in their site (like https://ift.tt/2JudAYW) and then it goes to the store page.

We have a promo code site and we want to know why these sites do this work and what is the purpose of this action?