But some pop ups deserve to be smacked down! And Google is on the case ... this article from TechCrunch explains all. It is a bit techy, but scroll down to the pics of a smart phone screen and you can see which pop ups are going to get penalised .. the ones you can't easily get rid of, the ones that cover content the second you arrive on the site, and mainly for the sites as they appear on mobiles. PS. "Interstitial" means pop up, in ordinary language.
My pop up is going to have to change, but I have until the end of the year to sort it out ... mine probably pops up too soon (though I have it on the max delay that app offers and it should only be popping up on your first visit) an dis a bit big (but it's the only size this app offers).
Anyway, pop ups are changing .. if you have a big pop up that pops up 'intrusively' as defined by Google you will need to change as well. No hurry ... but prior warning.