The Complete Guide to WordPress Popup Plugins

Most site visitors would tell you that they hate popups, but we still see them everywhere and the reason is quite simple. Popups work really well when it comes to retaining visitors and pulling in big crowds. Popups help increase site conversion rate, which is quite high in some cases (as high as 300%). However, popups should be used very selectively and carefully as they can also negatively impact the user experience and do more harm than good if not done properly. Another issue associated with popup plugins is their negative impact on site performance and page loading. Most sites use popups to convert random visitors into email subscribers, but they can also be used to highlight important content and promotional offers. Why Use Popup Plugins?
Poorly designed and executed popups can cause issues that not only harm SEO, but may also result in annoyed visitors and poor user experience. With thousands of free and paid options available, it often becomes a daunting task to pick the right one that helps convert random visitors into subscribers. Many plugins also offer unique features that allow you to differentiate your website from the rest and stand out from the crowd. Popups plugins
Source: https://managewp.org/articles/15732/the-complete-guide-to-wordpress-popup-plugins

source https://williechiu40.wordpress.com/2017/07/27/the-complete-guide-to-wordpress-popup-plugins/