All pop-ups on your website should make conversions on your website. Sell a product, make users leave their contact information, or even keep users from walking away from the website without making a purchase. Here's an in-depth guide on what pop-ups are https://claspo.io/blog/what-are-pop-ups-a-definitive-guide-with-examples-best-practices/ how to use them on your website, the best methods you have to use for conversions, etc. I used these tips when I started my website.