Popups, if used in smarter ways, are very useful & best practice to be used in websites. It can be used to achieve various goals for e.g: online advertising, announcement’s, to make user aware on special discounts and to collect user email addresses.
Test after test has proven that popups work extremely well. In one test, popups drove 1,375% more email captures vs. a sidebar opt-in form.
In another test, a website was receiving only 10 to 15 subscribers per day despite getting over 44,000 unique visitors each day. After implementing a popup with a 60 second delay, they began receiving 100-150 emails per day.
More & more number of blog websites are using popups. Yes it works well.