#2
it adds reverberation, like a kind of ambeince that naturally get from sounds bouncing off od the walls when you play.
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Last.fm
#3
Echo stuff.
I'm not very active here on UG currently.
I'm a retired Supermod off to the greener pastures of the real world.
#5
^^ Basically

Not echo though, that's delay !!

Advised against if your a uber-thrash-death-black rhythm guitarist...... it'll mess with your tightness !!!
Tone is all ...... well probably 75%, in your fingers.
The rest depends on your wallet's thickness !!

Keep the faith, baby!!