AndyGray

The G-string basically has two functions. The first tracks your guitar signal and the second cuts any unwanted sound.
If you are wanting a noise gate which cuts unwanted noise on a high gain channel but doesn't need adjusting when you're on clean, the G-string is the pedal for you.
WARNING: This will only reduce noise from one source. If you're getting a lot of pre-amp buzz then the setup below is perfect.

Guitar > ISP Tracker > Pre-AMP > FX Loop Out > ISP Gate > FX Loop in > AMP

I use it weekly at gigs/practice and it cuts all sounds on the clean but still allows for long drawn out chords on the clean channel.

The only other thing I'd like to point out is if you're planning on playing your guitar with the volume knob very low it doesn't really work.