Pop-ups are a controversial subject. So much so that the inventor even apologized for them.
However, it's probably fair to say that the worst of the stigma has worn off. The days of playing whack-a-mole on unwanted pop-ups have come and gone, and it's now common to use them for newsletter sign-ups, and even upsell offers.
They've been shown to double some people’s conversion rates for lead generation (pretty amazing, right?). But, still pop-ups can be really obnoxious if you do them wrong.