This feature detects whether the client is running an ad blocker add-on. If so, sending that user code for ads (such as AdSense) is going to be useless... however, you may have a way to advertise with a simple picture from your website, which should not get blocked.

This specific plugin only determines whether an ad blocker is running or not and saves the information for later so we can avoid sending ad code which won't work with such clients.

The flag can be checked on the client side (with JavaScript) or the server side (in C++) and your plugins can depend on this one and react accordingly. The client side is required too because the first time a client loads a page, we cannot yet know whether they have an ad blocker or not.