Mono versus Stereo Effects
The effects-chain usually contains a mono section followed by a stereo section. The distortion units, for example, are mono, so it is best to have them at the left. Stereo units, such as Chorus and Reverb, should be at the far right in the FX chain. Everything to the right of the first stereo effect in the effects-chain will be stereo, any subsequent mono FX will be duplicated for stereo operation (hence twice as expensive).