Adding a popup box or banner to your website will cause an increase in bounce rates.
Imagine you walk into a store in the mall. You see some products or services you may be interested in. But before you take your second step a person jumps in front of you blocking your view of the store and asking for your person info and if you like to join their newsletter or purchase a promo item.
I don't know about you but I would leave that store with a negative first impression.
Now, it is okay to have a popup at the appropriate time. Delay the popup for at least 30 seconds or set it to trigger when the visitor is about to leave or if they visit a specific page.