The majority of modern web browsers come with popup blockers that take care of several common types of popups that you may run into on the Internet.
You may encounter sites and services that use different techniques to spawn popup windows in the browser that are not blocked by the default popup blocking mechanics.
One basic example are popups that are launched as soon as you click anywhere on the site.
The extension displays an icon in Chrome's address bar that highlights the number of popups that it has blocked on the active website.
You can click on that selection to see all those popups, which can come in handy if you need to open one of them. Some websites use popups for certain features, such as downloads, and if you block them, you won't be able to use those functionality.
A site that bombards you with popups is the live streaming website Livetv which not only uses them to launch the player window, but also to spawn a lot of popups regularly while you are watching the stream.
You will notice that the Chrome extension blocks the streaming window popup on the site as well, but that is easily fixed by launching it manually with a click on the extension's icon and the selection of the right blocked popup window from the list.
Popups are not spawned anymore in the player window and while you will still see lots of ads, it is less annoying than having to deal with ads and popups on the site.
If you do not like the "block all" approach of the application, you can alternatively switch to a blacklist only setting. Here only popups that you have added to the blacklist are blocked, while all others are allowed.
Since it is possible to open any blocked popup window with a click on the extension's icon, you are not losing any functionality in this regard. And if you run into the same blocked popups regularly, you can easily whitelist them to make things more comfortable for you.