What are Pre-faders on the mixer?

[William Choi]

OK, I know Post faders aux sends are for FX like reverb or flange. Because while having the FX unit at its full blast, you're supposed to ease the Post fader little by litle until the right amount of Reverb or whatever the Fx you're using can be heard.
Now where does the Pre Fader come in?
Im thinking that they're used for Compression mostly. Am I right?
So if you're using pre-faders,pretty much you're using the pre-fader nob to control the complete signal going into the compressor (never mind the level nob) and all you're getting is the wet signal?(because:Im not sure: the level nob is bypassed? Why are the mixer company paying so much attention to people who want to modify it into two post-faders?

[Dom Franco]

Pre-fader sends take the signal from the input of the channel of the mixer and bypass the "Faders" (The long slider type volume control).

Pre-fader sends are often used to set up a headphone mix or a stage monitor mix in a live situation. This way you can allow the players to listen to their own preferences in the headphone mix, without affecting the master mix.(Fader settings).

You will need to route the pre-fader signal to it's own separate amplifier, and then to speakers or headphones.

Dom Franco