Tunghaichuan is right, by putting it in the FX loop, it is merely another master volume- although one you can control from your foot which might be useful in a couple of applications- such as being far away from your amp on stage. But otherwise, not many things you can do with it.
I prefer to use one infront of an amp for volume swells when the guitar im using's volume pot is too far away to do it manually. Try this with a delay before distortion/od and you get some pretty cool sounds.
Guitars: Squier '51, Fender Classic Player's 60s Strat, Epiphone Dot, Ibanez SA260FM (Bareknuckle Nailbomb/Trilogy Suite p'ups)
Pedals: Fender Pt100, Tech21 Double Drive, BYOC Mighty Mouse, EHX Stereo Pulsar, Boss DD-20
Amp: Blackstar HT-20 Studio, Fender Blues Jr