Application of notch filter in radio receivers
For a given system and application, especially wideband sytems, sometimes we can consider dominant interfering signals. So a notch filter is tuned specefically on the frequency of the interferers. In such case, we remove part of the desired signal's energy as well, however, the narrowband interference wich is usually much stronger than the desired signal (in a narrow bandwidth only) is removed and its harmful effect is prevented.

As an example, you might have heard of ultra widebsnd systems that span over a large spectrum between 3.1 Ghz to 10.6 Ghz. They may interfere with WLAN at 5.6 Ghz. Therefore, the UWB receiver can deploy a notch filter at 5.6 GHz.