The use of pop-ups (as well as overlays, modals, and interstitials) is hotly debated among 'Net professionals.
There's no denying the approach can be quite effective for increasing conversion in whatever form they may come. This Sumo case study from June 2017, for example, claims the conversion rate of high-performing pop-ups is over 9 percent. That's almost impossible to ignore for Web professionals looking to squeeze every possible conversion from their audience.
Due to often poor execution, however, the use of pop-ups can easily annoy users and drive them away. What's more, the approach (be it through overlays, modals, or interstitials; essentially anything that interrupts the flow of a user's journey to satisfy a brand's objectives) can cause irreparable damage to search engine optimization campaigns.
If you're currently using pop-ups however, there's really no reason to panic - you just need to know how to get away with it so you a) don't incur a penalty, and most importantly b) don't aggravate users. Keep in mind that Google's "interstitial penalty" is really only limited to mobile so it is just fine (for now) to keep using them on the desktop experience provided to website visitors.
With Google's mobile first index likely coming in early 2018, now is the time to make sure you're using this approach the right way. So what's the best way to get away with the use of pop-ups?
TONE IT DOWN: Pop-ups are often seen as overly aggressive because they make the digital experience inaccessible (the reason consumers intended to visit in the first place, be it content or products). It's almost always best to get the user to that experience faster and as such it's suggested that websites avoid using pop-ups that force users to close them out or dismiss them to keep reading. It really comes down to not interrupting users during their journey and making them easy to close or remove.
TUNE IT UP: With all of the overly aggressive pop-ups removed from the website, consider approaches which fine tune the use of pop-ups. The use of banner ads that don't take up more that 10 or 15 percent of the screen for example is perfectly fine. Websites may also want to consider switching to timed pop-ups (those that appear after a certain amount of time), activity-based pop-ups (those following a certain number of page views), or exit-intent pop-ups (triggered when the user engages in a behavior which indicates they are leaving such as selecting an outbound link or hitting the browser's back button).
There are several other approaches that will enable website to keep using popups that are worth mentioning. For example, it's possible (with a little creative programming) to only show popups when users come from sources that aren't Google. Did they arrive from social media sites like Twitter or Facebook? Show them a pop-up. Were they referred by a partner? Go ahead, show them a pop-up.
No one can tell you if using pop-ups is going to be effective. You'll need to test with your own audience to determine the impact of the approach on your own digital property and experience. That being said, however, by following some of the guidance provided here, you're "more" likely to get away with it without annoying users or Google.