The Dry/Wet System: How Pros Run Their Guitar Rig.
The Dry / Wet system is a kind of stereo operation. But here, one speaker gets the guitar signal which only contains the basic effects such as distortion and WahWah (dry). The other speaker gets the signal with all the effects – especially reverb and delay (wet).
A “real” stereo sound with lots of great effects is usually counterproductive in a live environment. If there is too much reverb, it becomes impossible for the sound engineer to mix a great guitar sound. It might sound good on stage, but the audience hears only squishy squashy tones since the concert hall comes with a lot of reverb itself.
However, if the FOH technician gets your dry signal in addition to the effect signal, he can work with the base sound and add only as much wet signal to the mix as necessary. Even stereo effects, such as PingPong Delays, only make sense when they are used very specifically and if your band works with an own sound engineer who exactly knows your sound.
The WET/DRY/WET system
If you nevertheless like to use stereo effects, you can go a step further and build a Wet/Dry/Wet system. This requires 3 cabinets and, besides your main guitar amplifier, a stereo power amplifier or two additional guitar amps. The center speaker gets the dry signal from your main guitar amp. The left and right speakers will get the stereo signal which is coming from your (multi-)effects unit.