what the differnece between putting an effect in the "effects loop" as opposed to putting one in front of a guitar?
effects loops are designed for modulation and time effects (chorus, delay, etc..) it basically skips the pre-amp

Epi Les Paul Std w/Duncans
Cry Baby From Hell
Marshall JH-1
EHX Metal Muff
MXR EVH Phase 90
Carl Martin Classic Chorus
EHX #1 Echo
Ibanez LU-20
Dunlop DCB-10
Crate V50112
Tascam US144

In the loop the pedal affects the sound after the pre-amp as opposed to before. This is geared more towards amps that have built in effects you want to use, like distortion but don't have effects like reverb or chorus that need to go after distortion.