It mostly depends on the kind of popup you set:
– If you create a popup with an “exit intent” trigger, you should set “1” or “2” display maximum per visit. You don’t want to bother your visitor 10 times with your exit popup if he likes to switch a lot from tab to tab.
– If you create a button widget (little button on the bottom left or right of the page) or an accordion popup, you can set an unlimited number of displays per visit, like “99” times for example. This gives the opportunity to your visitor to click on it at any time without bothering him during his visit.
– If you create a popup overlay that will cover what the visitor is reading (a part of the page of the full screen), you should generally set “1” display per visit. That’s why it’s important to choose the right trigger and/or the right “minimum of pages view” before displaying the popup, to convert a maximum number of visitors.