Typical use for a pre-fade send is as a monitor or cue feed; setting up a separate mix for the talent, for instance, that’s not affected by changes in the channel faders. You can also use it as a pre-fade effects send like if there is an effect you want to keep feeding regardless of the channel fader position. An example is an echo effect you want to keep repeating even after you fade out the dry source whether it’s a live source or the playback of a track...or a reverb and as the song fades out all that’s left is the reverb.