This is to inactivate the limiter section of the plugin completely. I personally recommend you turn the ceiling knob way up. This is useful if you have an uneven noise and need to take into account mini volume spikes in the audio. In the Fruity Limiter, there is a noise gate section. Open up the mixer, go to slots, click on an empty slot, and in the list choose Fruity Limiter. As this plugin contains several different modules you need to be careful with its settings. However, there is one important thing you need to know in order to not affect the sound in the wrong way.
FL Studio has a built-in Noise Gate which is accessed through the Fruity Limiter plugin.
