I understand what Aux-sends are and are used for but I cant seam to figure out what a aux-return is and/or could be used for. I cant find anything substantial on a quick search.
Suppose you want to use parallel audio effects (i.e. typically reverb, delay or sometimes chorus: effects that just add some "dependent extra signal" rather than "destructively" modifying an input signal). There are two obvious ways to do this:
The latter apparently seems less intuitive to many people at first, but it's actually far more natural: again, we're talking about parallel effects here. And it has a number of advantages:
In principle, there's no need to actually use Aux returns for this kind of parallel processing: you can route the signal back to any normal line input, sometimes it is in fact necessary (like when you need to use the console's EQs); but more often you'd pretty much keep the controls of these channels neutral anyway: the sound modifications can often be done better in the FX processing unit, and the levels are usually controlled pre FX (per channel!) rather than post FX, which has normally the same result since parallel effects are almost always linear. And often on analog consoles, you don't have such a lot of input channels that you can afford to spend any of them on FX returns. But then there's still these nice little Aux return channels, which do just what you need.
Of course, you can also use Aux returns as simple little line input channels, if you've already run out of these and don't need preamp control, EQs etc. for some signals.
I have seen it used to provide an effects path (aux-send : effects : aux-return)
From Wikipedia's Aux-Send article: The signal from the auxiliary send is often routed through outboard audio processing effects units (e.g., reverb) and then returned to the mixer using an auxiliary return input jack, thus creating an effects loop. This allows effect to be added to an audio source or channel within the mixing console.